This is a digital copy of a book that was preserved for generations on library shelves before it was carefully scanned by Google as part of a project
to make the world's books discoverable online.
It has survived long enough for the copyright to expire and the book to enter the public domain. A public domain book is one that was never subject
to copyright or whose legal copyright term has expired. Whether a book is in the public domain may vary country to country. Public domain books
are our gateways to the past, representing a wealth of history, culture and knowledge that's often difficult to discover.
Marks, notations and other marginalia present in the original volume will appear in this file - a reminder of this book's long journey from the
publisher to a library and finally to you.
Usage guidelines
Google is proud to partner with libraries to digitize public domain materials and make them widely accessible. Public domain books belong to the
public and we are merely their custodians. Nevertheless, this work is expensive, so in order to keep providing this resource, we have taken steps to
prevent abuse by commercial parties, including placing technical restrictions on automated querying.
We also ask that you:
+ Make non-commercial use of the files We designed Google Book Search for use by individuals, and we request that you use these files for
personal, non-commercial purposes.
+ Refrain from automated querying Do not send automated queries of any sort to Google's system: If you are conducting research on machine
translation, optical character recognition or other areas where access to a large amount of text is helpful, please contact us. We encourage the
use of public domain materials for these purposes and may be able to help.
+ Maintain attribution The Google "watermark" you see on each file is essential for informing people about this project and helping them find
additional materials through Google Book Search. Please do not remove it.
+ Keep it legal Whatever your use, remember that you are responsible for ensuring that what you are doing is legal. Do not assume that just
because we believe a book is in the public domain for users in the United States, that the work is also in the public domain for users in other
countries. Whether a book is still in copyright varies from country to country, and we can't offer guidance on whether any specific use of
any specific book is allowed. Please do not assume that a book's appearance in Google Book Search means it can be used in any manner
anywhere in the world. Copyright infringement liability can be quite severe.
About Google Book Search
Google's mission is to organize the world's information and to make it universally accessible and useful. Google Book Search helps readers
discover the world's books while helping authors and publishers reach new audiences. You can search through the full text of this book on the web
at |http : //books . google . com/
RATI ONAL
RECREATIONS.
VOLUME THE SECOND.
CONTAININe
EXPE RIMENTS
I N
OPTICS, CHROMATICS,
AND
ACOUSTICS.
A.
R ATI ON A L
RECREATIONS,
b which tke PRINCIPLtS ttf
NUMBERS
A N P
NATURAL PHILOSOPHY
Are dearly and coploufly elucidated»
BY A SERIES OF
EASY, ENTERTAINING, INTERESTING
EXPERIMENTS.
Among which art
All thofc commonly performed with the Cards. ^
By W. H O O P E R, M. a
^ ' "/ \ VOL. IL
—- ^' LONDON,
Printed for L. Davw, Holborn j J. Robsom, New Bond-fcwt ;
B.LAW, AvcBUuy-lanes and O. Robinson, Pater-nofttr-ron^
.■^•' -•>« ■ •■•4
'.'*-• fc.. ■
» • • • _• •
, • • •
DESCRIPTION of the PLATES.
PLATE 1. p. 8.
TJ^IG, I. Shows the manner in which the rays
•*• of light converge and diverge.
Fig. 2. Different objeds feen under the fame
optic angle.
Fig, J. The rcfradtion of a ray of light, AB, in
pafling through different mediums.
Fig. 4* The different forts of lenies.
PLATE IL p. 12.
Fig, I. The difpofition of the lenfes of a com-
mon telefcope. AB the objeft-glafs, CD the eye-
glafs ; O.I the objedt, which appears inverted at
£, and magnified.
Fig. 2. The conftruftion of a terreftrial te-
lefcope, in which the lenfes CD and EF are added
tothofe in the laft figure, and by which the objedt
is made to appear in its natural pofition.
Fig. 5. Shows the ftru&ure of a reflecting te*
lefcqpe. GH is a large concave metalline mirror^
Vouil. . a per*
u
DESCklPTlON OF
perforatefl at r, b^ which the imifge '6fariobjefty
entering at the eftd of the tirbe 0E/ftlefleded to
the ftnall mirror f^ placed on a ftatid, and by that
to the ghffes B and A; which Convey it* to the
eye in an ereft pofirion. *
Fig, 4. The conftfuftion of i double micro-
fcope. AB the objed glafs, and CD the eye-
glafs : gmb the objeft, and GH the image, which
appears inverted and greatly rri^^ified.
PLATE Iir. p. 33.
• ■ '> »
Fig. I, r% a'vieffel with wateiv by the refiac-
tton of the light** through whkh three pieces of
money E^ F, G> are feen at the point where they
were invifible before the water was pomced inta
the vefiel. ''"'' ' '
Fig. 2. Three ffftal! pieced of paper A^B, C,
being'fiflick againft the watl, the image of ooe of
them 'will always fall on the optic lierve at D,
and tTtefefoi-e be invifible.. --
Fig. j; The ^rtafele caitter* obfcura*: £ is a
' pfarfc^of glafs placed in the frame ABCD^to which
the hnagfe crf'the dbjefts that entct the tube Q^ are
reflT<Sed by^the nWrroT N. Thef. four -legs and
the pieces thSt-^drtiptofe the cafe H^ hav^ hinges,
by which they fold up^
Fig; 4. ThcMTTa^ Manterrt* "^^ ABCD is a tin
bc>x, ^in oyae !^gd^^\yKl^cl>.i$.a. OMficayc inirror G 5.
at ilM^}9flp9liw:^5^ if!^^oft\?^^9fls^Jf^,,^^^^
it a tin tube O^ that has an opc^p^ingj^i^, ^hcoiigh
which are paiTccI: tjfee ^jUfles chat have the otjefts
8 painted
^j^% jp±a:^es.
m
pi^p^y^ fi^an. In the tube O is placed another,
Ji^if^tij^fTM^vcaWe, and chat contains two Jenfes P
'^t^,^y})j.^h\c^ the objcdljs.on the glafies are
; t^own /3[r> ;))^ wall : K is. a lamp, and E, F the
funnel by which the fcuoke .conies ouc, and it$co-
yejT that keeps in the light.
Fig, ifi^t'^ art two plates of glafs, to pafs
through the groove in the magic lantern at the
fame tirn^, ^^nd by which- tl^e appearance of a
tempeft is to be exhibired%
-Fig. y, i$/%box: rhac contains a cbaSngdifh,
toiij^ihe/mofcc^J^f which, tHatcoi^iesQut^t the top
.ofthc>JbG)*- AB/fbc figures, pf, a magip Jautern are
Fig. 4. A machine for reprefenting.a phan-
4k>m: widMnoici^.. placed a magic lautqrn, the
images 5£r!i^hicjh being refl^icted by tfee mirror M,
* pa&OMC ^X:M opening E> in the top of the box,
and are thrown on the fi^oke of a cbatingdifh
Ijaaccd »p©a i^ whicre . they are vifible.
/ JFig*:5;i A large magic lantern for, exhibiting
tt> Qiagioal tbe^tre^ In the tube H are feveral
=: grooves in different directions, by which difFcrcnC
^•glafles are pafled at the fame time.
; ,. (i •; . P LA T E V, p. 66.
^^''F%/i. Rcpfiefentation orf^ objeft refleded
'%i'j>tifn'to1rmf. 'A thebbjcft, Githe mirrorr,
m^^iiiik^i. ■ ■"•••■ ^-- -
■ t!- ^h jr/;^:i Xil.. ^•.:.. . :^ i'^l^i.- r -f^ r: •• Fig,
iv . PESCRIPTION, OF.
Fig. a, G I is a convex mirror, A C tl>c ob-
jed, and DF the image.
Fig- 3» 01 a concave mirror, AC the objed,
DF the image, that appears behind the mirror and
eredt.
Fig. 4. GI a concave mirror, AC an objed at
a greater diftance, than in the laft figure; DF the
imngs before the mirror, inverted and diminiflied.
PL A T E Vl. p- 70.
Fig. i. The bok for the boundlefs gallery :
EF two pafteboards cut through, a^d jpaintcd on
both fides -, D a pafteboard painted' on one fide
only, and placed before a mirror at that end of the
box ; C is the hole by which the objects are viewed.
Fig. 2, and g. The painted pafteboards to place
in theb6xi Fig. l.^
Fig. 4: The box for the four liiagical mirrors.
A BCD tht body of the box^ againft whofe four
iirfides the hiirrors are placed. AEBNLI a frame
of glafs cdnfifting of four inclined plates, and one
at toptUic is horizontal ; by the latter the images
placed on'tht bot.tbfrt of the box are feen reflefted
by the mirrors. -
•Fig. ^. A j^knfor difpofing the objedbs in the
box, Kig:^4. ' :
,, / 1^ L A T;E VII. p. 79.
Fig. I • ^The enchanted palace. Againft the fix
pillars mirrors are fixed, that meet in the cen-
tner, and between each triangular divifion objefts
'are placed, that are reflefted by the mirrors.
ABCDEF is the plan of the bafe of the palace.
THE P L A T E S. V
Fig. 2; is a"lqbii*e on Whrih^' Tegiilkr figure is
drawq^ tljat when transferred to the correfponding
(fiViiions or Fig. '3, appears deformed, but when
fcen in a ^mirror placed at FG, frotp a point over
^9^^ exa^Iy the fame as orj Fig. 2.
"rig, 4. The magical dial. In the'drawer His
placed the dial Fig. 5, whofe index is a touched
netdle that ii^ moved by a magnetic bar under the
dl^l-plate, "At I another dial, Fig, 6, is placed,
whofe ihdfex IS likewife a touched needle, and is re-
gulated by that on Fig. 5. At M is an inclined
mirror, that, reflcfting the dial placed at I, makes
itvifiblfe at an operiing in that pentcr pf the dial
at the top <;>f ^ig, 4. _ ^ I
/'.EL A T E VIIL p. 86.
Fig. I. The box of divination A BCD, in
which are placed the tablets 1, 2, 3, 4, that each
Cfntains a magnet placed in a different pofition^
^^.*g 2,^ the table, under which is a bfafs rod
th^t has four pivots, to which are. fixed the four
pa^d^board circles P, Q, R, S, Fig- 3. MN is an
incUned^nirror placed in a dra\yer under the table.
Fig. 4, is the top of a box, that ha3 three holes,
aini 9iver ,th^m are placed three per fpe^ftives like
Fig.. 6. Each of thefe perfpedivcs is fixed on a
hollow pedeftal,and contains ^ mirror E, by which
the objedts on the circld Fig. 7, that' is put at
tbtt bottom of the box, are feea at D. There is a
imgnetic bar i concealed in the tabie^ on which.
^1y)\<:-(> -'^■''' - — * ■ a 3" tht
.aiorii/n ■■ '■'■: . ■... ■..■•• •. . . ■ • ,1^
vi, DE^CitiaPTiIOH.fOT
the bp^,i§^pl^c^^^v ^t moves the cifcjc Fi^ryj^.
by the needle in the middle of it. . r. . r
JP^SrJfeo^. *.^<^.lH9^n ^placed on the ^middle df
the bqxy. and '^n whic)i ihc fp^ftators fccm to fe^
the objcAs ftpwn by ijhe perfpcAi^rea.
•PL A T E IX. p, II^.
Fig, 2. The box for the animated optic balls.
IM the inclined planci /down wh)ch the ball O
runs, and through the groove P, to the hole at the
end of :ohc box. RF is the mirror that re-
fleds tl^uAcHned plane and the paintings in
the box tQ chcglafsratE, and which is rcprefent-
ed by Fjg. i. T the inclined plane for 4 double
refieftioni .Ffg* 4, j-^/^nd 6, the machinery that
raifes the t>all to xht top of the inclined plane.
Fig. 3. Thcpaititing on the inclined plane,
■ 'Pi: AT E X. PviiS, ;
Fig. T. The penetr^ipg perfpcdl^ive^ .FandG
are two moveaole^tubes. O, P, Q, R, are four
inclined ipiriprs>, .^^ijac i^efled the.obj^ftj, enteriog
.Fig. o, , Xlieqiagifian's o^irrprs., . CD and.EF
two holes in.tt^^ Witinrcut; H an4 I. the |wo mir-
ror§^ by ^hkh the i^bjeds entering one of> the
h6]]}sis reflede^ to theociier;. . ^ . ■,. . ..,.,;. .
"Fig. 3, Theencfii^^tt^^i^-mirro^*,. AP'^^CR
the, two mirrors placed crofs the box in a diagonal.
Hand
tors fee each other. = ' • -^ "• ■ - • '
•Fi^.'g;'^he m^rhine for Ifeihg ari ir¥egular fi-
gcM inrra'iimitefpfyitig giafi*' ' A B .Ihc-ffand
with the glafs fixed to it i 1% thef Hale througE
which the image is feen. Fig. 6. the ruler for
drawing the jjc&e&ion on jhei boarcj. D? E F G,
Fig. 7, 8, and 9, projeftions of the glafs.
; i:. ;P L AT E XI. p. 126.
Fi^rji The xylindric rtutror for viewing an
irregular figu!^ diawb on the iboard FG^ fr^m the
poi^^crf'rywwJEi^ whei'c it appears n;gul&r.
Fig* 20 The method of dividiiig the diaineter
of a, cifckiintx) a number of parts, which are to be
transfencd; »:thfc cylinder, and refkded on the
board^ fat ^rlaeing the irregular figure.
Fig. 3. The plan for drawing the regular figure.
Fig. 4, 5,<and 6. The appearapcesj of a bottle
of water before a concave mirror^
' - V p'^t E ^XlL ' p, 134. ;
Fig* 1. The perfpcaive mirror. H tlie ciin-
cave mirror, IL the blacked paftcbbard'foi'' re-'
gditihg'tlS^ view;' C the aperture for viewing the
obj^fts'pliced beneath it, in* the riiirrdri^/
dPig; 2. ' A' rfndfi two conda^eirtixxbri' for firing'
combuftible bodies at a diflraticel' C'il^D X^tlt
fd^iVte«#Ificfithe'bbdSesai^ placed *^^
^.Mo-t ->:. •.•■■• ■ ■-^■■■- ^•:^.^•■ '■-'- Fig.
1 1
viu DESCRIPTION OF
Fig. 3. The ipafihiftery. for the real apparition.
C an inverted objeft placed under the hole in the
partitioh AB, and whrch^ by the reflection oif the
concavc'niJrror, appears ertft at D, on the outfide
of the partition.
i>.L A T E XIII. p. 160.
Fig. f. The ray of light C, p^iGGqg through the
window-fhutter AB, is rcfradbed by the prifm
D EF, into the fpeftrum P Q, that exhibits all
the fevcn primary colours. ■ ' >'
Fig. 3, and 4. The glafles and painted papers
for repftifenting the feverai colours and their gra-
dations.- ■• ■•'■■•"■• ■ ' , ■''
Fig. 4. The magical prifm. Al& C a large
prifm, by which a ray of light is rtfrafted, and
falls on the fmall prifm DEF, that as it revolves
on its axis-appears oJFdfReredc dolours.'
Fig, 5. The pdfip^tic camejra qbfcura. F/
two rays of light tli.ajjbein^ refra^^^ by.thc prlCms
A, B, C, and a^h^c^ form the jTpeftrum MN,
which appears to be, oaioted with all the original
colours. ;^ , :
"P L A T E ! XIV. p, 166.. . , r
Fig. I. A ray of light largely refracS^ed into
the fpeftruni PT^ the divifions of whofe colours
conefpondim ti(6 divigon^ of a chord for the notes
of-the oa{ave.'.v/,^ y^ ''. ■ ^ " •' ^^^' '='■■''■
Fig* fl^itad' J. THd machine for ejihibitfeg to-
:...■•-■" q-l;' i*n-a.:: P-Ii,'A"T'E S." •••■ ix
lorific mufic^j ^^Irlie fhaded pjarcs in Fig„ 2,,rcprc-
fent the colours. , t is the fcrew on .which :it
turns,' G a wheel that is moved by fhQ cndlels
fcrew ^H.
Fig- 3j is the cafe that contains the cylinder.
The eight fhaded parts in the middle arc the
holes through which the colours on the cyUn*
dcr arc fceil ; t> the handle th^t "turns the lendlcls
fcreww
P LA T E XV. p. 1734 v
Fig-jij, 2vahd3- The piaqs for drawing an ir-
regdlar figure that will appear regular when feea
through a hq^c in the (land Fig^ 4, placed in the
proper poCtion. . m,
PLAT E. XVI. p. 178. ..
Fig. tV 2 J ahd 3-' The plans for drawins an ir-
regular figure, which when feen Froni two pppo-
fn6 points of view, prefents two regular figures.
Fig. 4» A pafteboard in which lines are cut,
and over them the paper Fig. 5, that contdns
the drawing h td be jpafted. '
PTL ATE XVIi; p. i8j, :.
^'^8* Wt*0^*^ The apparatus for dmwing an
irregular figure on the bafc of a coney^ebat ap-
pear^ rc;gi»ilfr fronx the point H ; FEG.thexone 1
MNE,tlic poficion of a glafs on which the regular
figure is drawn, and that is projected on the cone
by
by tte( Jarnp Figu 2| when placed in, the ropm o(
theftanciHU . .i . / «^ '\ ,; \
F'S* 3« The pi^chine for drawing any objeft
corredly, EAC the tube for yie^ing.theobjeft i
BFEKJ' the franje^ fliown more dearly in Fig, 4,
by which the parjKi qf cl>e otyed are transferred to
fimilardivifioos on a^ paper* , ,^ ^
i*^*g^ 5* The box for illuminated prpfpefts*
EFGH the back of the box in ^Ijic^ the prints are
placed^ and behind (hem lamps prcapdics*
PLA TE XVIIir^p^^
Fig^i^ Ihows the :alternatc vibratjtonsiaf achord*
Fig. 2* A chord fo divided as to found the fc-
ven concords. -
Fig. 34 The apparatus for the vectofal fym*
^ phony.. . A. the vane that gi>te5» motion to the
machine, ; C,D, G,.H, I^M, wheels and pinions
that fcrve to move the barrel NO, in which are a
number of ftops, that ftrike a fet of bells.
Fig. 4/The whifpering gallery. A the point
from whence the found proceeds, and Is reverbe*
rated by the points DEFG, to C,^ where it is plain-
ly heardi
Fig. 5. The converfive ftatue* AB and GH
are two concave mirrors ; C and I their centers ;
EF a partition that has a hole, through which a
found iifuing at I, is diflinfUy heard at C«
PLATE XIX. p. 240.
Fig. I, (hows the mechanifm of the great organ.
0,0, are the handles that pufh down the bellows
TT:
'^ •F1?l ^^Vi'iiife *^ htfwHes^ tlfiit tWttthe rollers
R. R, that by means of the arms <l fi pull Dut
'^ tiu? iliddS /,^ I', and givfe' liberty to the pipes
pJi^flbM'iVjjr'rfny rcw hdleaf to fouiid } C, D,
' ^ ]^ occi- arette keys, whieh beti^ pirtdown open
thisf VafWs ^V; chat adtnk ffte 4if to the pipes :
HIKK is a wind-cheft, that'teoclres the air by
^'^vt^^Y^^i^ X is a fliite-pi|)e of wood 5 Y
' « thiAfeii-T{>i^bf metal j 2 a flute-pipe of metah
Figi 2'/flid>*s^ the conftrudHon of a valve, with
the wire that open$, it apd the fpringthat (huts it.
Fig. 3. I^he infide of a Aute-pipe. A B the
ftioti -BD thtt body; EF the partition; EC the
ttiouifc^
Fig. 4, A reed pipe ; AB the foot ; CD the
^altot^reedU KIL. a plate of copper fitted into
the mould? ar \h\xx: being loofe at its extremity K,
lAie; ^r imakes it. fliake againft the reed.
:/:«;q or;-) i-i .,^ . ;■ .
■-■.»■;• •'j^i-r ^j. ]'''.: i: ■ ' ■• .
■: <-'q >.{ r ::',)}'■■■. , .., ,
V; A
RATIONAL
n
' i > J •!
•T « I r
RATIONAL RECREATiaNS.
OPTICS.
r "Inl H £ fcience of optics explains thd
I nature of vifion,- by invcftigating
the caufes of the various pheno^
mena that arife from the refradion arid
refleftion of light. It is divided into
Dioptrics, Catoptrics, arid Chrotaatics *•
'The firft treifs of refradtion ; the fecond^
of refiedidn j and the laft, of colours,
GENERAL DEFINITIONS.
i*\\rhen the rays of light that iflud
from any body, continually recede from
• Thefe terms are derived from the Greek; the
firft from the word dioptra^ a peifpe<Slive glafs; the
fecond from katoptron^ a mirror j and the laft from
thromata^ colours.
You IL » tech
2 R A T I O N A t
each other, as the rays A B and A
(Plate I. Fig. i.) they are faid to di-
verge.
2. When rays in their progrefs draw
continually nearer to each othef , as the
fays BF and C F, (Plate I. Fig i.) they are
feid ta converge
3. That point in which converging ray«
all meet, is called their focus^;ta» the point
F, in the fame figure.
4. An optic angle is the fpaice contsiined
between two lines drawn from the extremis
tiesr of any obje<3: to the eye. Thus A £ B^
or CED (Plate I. Fig. 2.) are the optic
angles under which the objeds AB and;
CD appear to the eye at E^ ^ .
GEEERAL
kfeCkfiATlON^; • 3
GENERAL APHORISMS.
\. The motion of light is not inftanta^
iiioiis but progreffiye *.
2. All rays of light naturally proceed
in right lines*
3 . No objeifi can be feen diftindtly at a
tefs diflance than about eight inched.
-.4. »Tcft produce diftind vifion, the rays
of light muft be parallel when they enter
the eye.
5* Rays of light that come fronj. a far
diftant objeA, are to be confidered as pa>-
rallel.
• 6;- Wherever the r^ys that come from
all the points of an obje£t, meet again in
* It appears^ by aftronomical obfervations, that
the rays of light are 8 minutes and 13 feconds in
coming from the fun to the earth, which are dif-
tant about 82 millions of miles; their progrefs,
therefore, is at the rate of about ten millions of
miles in a minute;, yet great as that velocity is,
the diftance of the largeft, that is, the neareft of
the fixed ftars, being four hundred thoufand times
greater than that of the fun, the light muft be
moi'e than dx years in coming from them to us.
B2 fo
4 RAT 10 N At
fo many points, after they hiave been made
to converge by refraction or refledlion,
they will there form an image of that ob-
je£t on any white body. ^* ■
7* Every object fecn by refradlion or
reflection, appears to be in that point
from whence its riys are laft rfefradted or
reflected to the eye* .*
8: The apparent magnitu4e.of a^y ob-
jedt is determined by the magnitude /of
its optic angle ; therefore the objedka A B
arid CD, (Plate I. Fig. 2.) which are feen
under the fame angle, will appear of equal
magnitude.
Thefe, and every other aphorifm in this
' treatife, are confirmed by all optici^l wri-
ters; vand may be demonftr^ted geometri-
cally: but as we fuppofe our readers, to
have no other previous knowledge than
that of common arithmeti<D, it would be
fuperfluous to infert fuch demonilrations
here.
DIOP-
UECREATTONS. 5
DIOPTRICS.
TNIOP TRIGS, as we have faid, ex-
plains * the feveral appearances that
arife from the refraifltion of light
, , £ F I N I T I O N S.
1. When a ray of light paflGi^g out of
one ttiediutW into anbther of a diflFerent
deiifity; is turned from that ftrait line
ih which it would otherwife proceed, into
one of i different diredtion, it is faiH to
he refraaed. Thus the ray AB, (Plate I.
Fig. 3.) hy pafling out of air into the glafs
OH, id turned from its natural courfe in-
^othatofCD,
2. Any fjplierical tranfparent glafs, that
^converges or diverges the rays of light as
they pftfs throtlgh it, is called a lens.
'' 3. Of lenfes there arc five forts: i.. A
j3laM or (ingle convexlens, which 19 plane
tOu one fide, and convex on the other,
as A (Plate I. Fig. 4.) 2. A double convex
Jens, as B. 3» A plano-concave lens,
B3 that
^ R A T*t O H A t-
that is, plain on one lide and concave on
the other> as G 4- A dpvible^cogicave, a?
D* And c. A menifcus, which is convex
on on6 (ide and concave on the othipr, as E.
4* The point C, rotind which the fphe-
yical furface qf a lens, as A Z (Plate I.
Fig. 4.) is defcribed, is c^ljed its center :
the line X Y, drawn »from that centpi; per-
pendicular to its two furfaces, is the axis;
pid the point V, to wjiich the axisi is
drawn, is the vertex of that len?, ,.
5. When the rays of light that pafs
through a fingle or. double conyepc le^sarc
l^rought into their fmalleft compafs, that
point i^ the focus of the |ens.
6. In optical inftruments that leps. \Yj}ich
is ne^t the obje£t is called the .pbj?<St-
glaf^^.aqd that ne?ct the eye, the eye^g^^s.
7. Th^ diftar^ce between t^e Une AF
(Plate I. Fig, 3,). <gind the . perpep^icular
E B, isj^all^d the.aflgle o:^ inpid^^cej and
jthe diflajice between the line CD.and Jhet
perpendicular 5 F, is c?Jle^ thg .fnjgle of
refraiaion. , .
flEvCR EAT IONS. ,7
^^^PHORISMS.
1. A fay of ligtt paffing obliquely out
>of one medium iato anoth'cr that is denfert
will be refraSed toward the perpendicular,
,as the ray A B (Plate I. tig. 3.) by pafllng
out of air into glafs is refradled into CD,
'toward thfc perpendicular B F. On the
xiontraiy^ a ray paffing out of a denfer in-
to a rarer medium, will be refracted
from the perpendicular ; as the ray B C,
paffing out of glafs into air, is refradled
* into 13 L ' '
2. The 'ingles 6f incidence, and refrac-
tion, when the lines that contain them
^re all equal, will have a determinate pro-
p6/ti6ri to each other, in the fame me-
' diums : 'which between air and water will
be as 4 to 3 ; between air and glafs, as
* 3 to'2, iifearly; and in other mediums in
JJrdpbrtion ^to their den Cities.
' 3. ^When an object is viewed through a
glaft ^/4^hofe; two furfaces are parallel, .it
'\v?Il appear of its natural dimenfions, its
fituation only being a fmall matter altered,
B 4 . In
$ R A TtO K At
in proportion to the ttficfencf^jpf the glaft*
^nd ^he obliquity of the rays.
4. All tl^e rays of light, whether di-
iverging, parjallcl, or converging, that fall
on a fingle or 4ouble convex lens, will
meet in a fopus behind the glafs : and the
4xftance of that focus will be greateft ia
diverging, and leaft in converging rays.
5. When parallel or converging rays,
fall on a fingle or double concave lens,
they will diverge behind it. If they be
diverging at their incidence, they will be-
come more fo by pafling through it.
6. When an obje£t is viewed through •
two convex lenfes. Us apparent length,
or diameter^ will be ^o its real length, as
the diftance of the focus^of the objed-glafs,
is to that of the eye-glafs^
By thefe,and the foregoing aphorifms, we
are enabled tp account for the various ef-
fe£ts of dioptric machines, as refrading
telefcopes, microfcopes, the camera ob-
fcura, &c. For example, fuppofe AB
|he objed^glafs, and CD the eye-glafsiof
a te-T
V./is
■I A Y oir A n - ■;
Plate,!.
RECREATIONS. 9
a teiefcope, (Plate 11. Fig. i.) and let them
be fo placed that the focus of each ma.y
coincide in the point F. Suppofe O I to be
a far diftant objeft, whofe rays are there-?
fore to be confidered as parallel when they
come to the glafs, (aphorifm 5, page 3.) the
two rays OA, and I B, proceeding from
the extremities of the objecft, and paffing
through the glafs A B, will meet and
interfedt each other in its focus F, and
pafs on to the eye-glafs CD, But F be-
ing alfo the focus of that glafs, thofc rays, by
paffing it, will again become parallel, and
therefore by (aphorifm 4. p. 3.) produce
diftindt vifion in the eye, placed at H.
Now fuppofe the diftance between AB
and F, that is, the focal length of the ob-
je<ft-glafs, to be 10 feet, or 120 inches,
and th6 diftance between F and C D»
which is the focal length of the eye-glafs,
to be three inches, then by aphorifm 6. p.
8. the apparent length or diameter of the
phjed will be to its real length as 1 20 to 3,
' or
gf^ 4P tQ I5 %t is, it» Mgt^ ^iil b«
laagnjjfied 40 ]^es, and cpnfequcn^y
jus fur%e> 7f it \>c ^ .%uafe, j,6pQ l:y»e§^
It is evident, frQWx ,the coajftruflion of
^is telefcope, that the Qt)je<3: rajift appev
= fo the eye i|sivertipd, bpt^^'it jls princi-
. ^paJJiy intended for viewing celeftial pbjeas,
ijth3.t cLrcjLimO^nce is not, much jregarded^
t .But whevii it. is applied to terrejftial yievs,
. j{wo ptibLCC'glaffes ^re added. One of whigh^
' as p. F, {Plate IL Fig, 2.) if placed ^t twice
jts focal diftance fjrom jpp,iaad the other,
GH, at. thp fame diftanqe ,fropi th^t^
Now the rays being made to interfei^: each
othef again, as is evident from the figyre,
the HQbje^ wiU then appear in its »^ra|
-pofuion.
Terreftria} teJefcopes are fometime§ wade
^ith one concave, eye-gla^ ; but ^s only ^^
linall part of an objed: can be feen by^thefe
at one view, they are but of little ufe in
laear and large objedb.
In
RfiC|R:EATip]SIS. ^ 4|
In like W4»ftcr fuppoife AB^DEi
(Pkte 11. Fig. 3.) to be the tijbeof a vtRcQr:
ii^ telefcope^ fheend PE bf ?ybich ip opja» :
let QIJ be a l^g^ cpncave mctaline mir-
|:or, peffbrtted at r. I, a fmaller mirror^
placed on the f);a)i4 K. Thefe mirrors ar^
to lie fo dii{K>fed that the focus of eacjti
Biiay fallj on the -point^ JNiow the images
j^f an objedyas aM^ eatepjoig the tube at
DE, will fell yppn the mirror GH in
the points cd^ md being i;efleded frogi
.jjbenqe to the focu? /^ the rays will there
Ipiteri^dt each other^ apd invert the imagp
aXigh. This image being alfo in the fo-
cus of the mirror I, after falling on it, in
the points i/^ will be refleded b^ck in
parallel rays^ whidi paffing through the
/hole rin the gye^^t. mirror, and;falling on
the ^onyex lens at B^ will again crofs each
..other in the :^Qcus of; that glaf^ ^ts^ which
being alfo the fpcua pf the lens at A, it
• wis fifomthencfi be, viewed by the eye at
L. .^ .The^ principal ^^o^llence.pf refleding
. ,|el^fcop!5S 4rjif?s , frovx the -br.ightncfs -^i
the
12 RATIONAL
Ae reflcdion, by which ohjcds appear fo
diftindl that an eye-glafs of a much fmaller
focus can be iifed in them than in others.
The magnifying power in this, as in o^
ther telefcopes, is as the focal diftance of
the objedl-glafs or mirror, to the focal
diftance. of the cye-glafs. But the latter
lieing fo much fmaller in this telefcope,
the magnifying power will be fo much
greater. Therefore, if the focal diftance
'of the eye^glafs be one inch, and that of
the objed-mirror 40 inches, the diameter
of the objeft will be magnified 40 times,
"and its furface 1600 times. A refleding
telefcope of 4 feet will magnify more than
'a refrador of 50 feet,
Suppofe, again, A B, (Plate 11. Fig. 4.)
to be the objed-glafs, and the C D the
eye-glafs of a double niicrofcopc. The
objedt-glafsmuft here be quite fmall and
very convex, and confequently its focal
diftance //, very Ihort. The diftance of
tte fipall oh^cdigmhy muft be very little
more
t A X * > T A tr
RECREATIONS. if
more than that of //i ia order that it*
image GH, inay be formed at a confider-
able diftance, and confequently be much
enlarged. Now this image will appear
diftinCt and confiderably magnified, and
that on two accounts : firft, in propor-
tion as the diftance K / is greater than /m ;
and fecondly, on account of the nearnefs
of the eye to the image ; for by apho-
rifm 3, page 3. no obje<a can be feen dif-
tindly by the naked eye, at a lefs diftance
^han eight inches, therefore if by means
of the eye-glafs CD, the objeft is made to
appear diflindt at the diftance of one inch,
it will feem eight times as large. Sup-
pofing, therefore, the focal diftance of
the eye-glafs CD, to be one inch, and the
diftance K / to be to /m^ as i o to 1 , then,
on both thefe accounts, the length of the
objeft will appear 8 times 1 o, or 80 times,
. and its furface 6400 times, larger than
when feen by the naked eye.
R E C R E-
i4 R A T i Of JJ A L
RECREAtldN I;
Optical illujiohs.
/^N the bottom of the veflei- ABCI^
(Plate III. Fig. i •) place three pieces of
money, as a-fhilling, a half-crown, an^
crown ; the firft at E, the fecond at F,
and the laft at G. Then place a perfoh
ait H, where he can fee no further into
the vefiel thain I : and tell him that by
pouring water into the veflel you Will
inake him fee three different pieces of
money; bidlig him obferve carefully whe-s
ther any naoney goes in with the water *.*
When the water comes up to K, the
j)iece at E will become vifible ; when it
comes up to L, the pieces at E and F
will appear ; and when it rifes to M, all
the three pieces will be vifible.
♦ You muft cither pour it in very gently,
or contrive to fix the pieces, that they may not
move out of their places by the motion of the
water.
From
kEt^REAtl(>NS. if
From what has been faid of the refrac-
fion of ligiit, the caufe of this phenome-
tiOTi will be evident : for while the veflel
is empty, the ray H I wilf naturally pro-
ceed in ia ftifaight line : but in prorp6rtiofir
ks it bfccomes immeifed ia water, it will b©
fteeeffarily refrdded into the feveral direc-
tions NE, OF, PG, aaid confequent^'
the feVdfal pieces muft become vifible.
RECREATION IL
Optical Augmentation.
npAKE a large drintinggUfs of aconi-'
cal figure, that is, fmall at bottom
and wide at top ; in which put a fhilling,
and 'fill t^e gk^s about half full with wa-
ter : tlien ptace a plate on the top of it,
ana turn it quickly over, that the water
m^^ nbt get oiiti * "^ou wilF then fee on the
plate, a piece bf the fize oF a half crown j.
iiliq fome^hat higher up, another piece of
the fizeof^ihillmg;
.:iiv i X
Thb
i6 RATIONAL
This phenomenon arifcs from feeing thcf
piece through tjie . ^onical fuffacc of the
water at the fide of the glafs, and through
* the flat furface at the top of the water, at
the fame time : for the conical fiir^u:^
dilates the rays and makes the piece ap-
pear larger; but by the flat furface the
rays are only refrafted^by which the piece
is feen higher up in the glafs, but ftill of
its natural fize. That this is the caufe
tvill be further evident by filling the glafa
•*vith water, for as the fliilling cannot be'
then feen from the top, the Idrge piece'
only will be vilibfe.
After you ha^e amufed yourfelf' with
this remarkable phenomenon, you may
give the glafs to a fervant, telling him ta
throw out the water, and take care of the'
two pieces of money ; and if he have no
fufpicion of the deception, he will be not
a little furprifed to find one piece dnly#
RECRE-
Rfe4D ^ t A f I b% S. 17
.:M . (\Qptical fub{ra5iwn.
'TC'GAI^ST the wainfcot of a room
fix three fmall pieces of paper, as
A, % C, (PI. III. Fig. 2.) at the height
of 'yoiir eye; and placing yourfelf di-
re9:ly before them, lliut your right eye
\ arid look at them with the left ; when you
will fee only two of thofe papers, fuppofe
A anci B; but altering the pofition of
yonr eye you will then fee the third and
one of the firft, fuppofe Aj and by al-
tering your pofition a fecond time, you
will fee B and C ; but never all three
of them together.
»
The caufe pf this phenomenon is, that
one of the three pencils of rays that come
from thefe objeds, falls conftantly on the
optic nerve at I) ; whereas to produce dif-
tinft vifion it is neceflary that the rays of
light fall on fome part of the retina E, F,
1 W^t^t^ C ' G,H.
i8 R,A T I O N Al*
G, H. We fee by this experiment, one of
the ufes of having two eye&j for he that
has one only, can never fee three objeds
placed in this pofition, nor all the parts
of one objedl of the fame extent, witUout
altering the lituation of his eye.
RECREATION IV.
Alternate illufiorr.
'XIITITH a convex lens of aboyt an
inch focus, look attentively at ^
filver feal, on Ts^hich a cypher. is engravi-
e^. . It will at firft appear cut in, as to thp
naked eye j but if you continue to obferve
it fome time> without chjmgingyour fitua^
tion, it will feem to be in relief, ^nd the ,
lights and fhades will appear the fame as
they did before. If you regard it with
the fame attention ftill longer, it will again
appear to be engraved : and fo on alter-^
nately.
^ If you look off the feal for a few
moments, when you view it again, in-
7 ftead
ileadbf feeing it, as at firft, engraved, it
^11 appear ia releif.
Jfi while you are turned toward the
light, you iuddenly incline the feal, while
you continue to regard it, fKofe parts that
feemed to be engraved will immediately
appear in relief: atid if, \^hen you are re-
garding thefe feeming prominent parts,
you turn yourfelf fo that the light may
fall on the right hand, you will fee the
ihadows on the fame fide from whence
the light coriies, which will appear not d-
JIttle extraordinary. In like maimer the
fliadows will appear on the left, if the
light fall on that fide. If inftead of a
fb.1, you look at a piece of mbney^ thefe
alterations will not be vifible', in whatever
Situation you place yoijriejf *•
* It has been fufpeSed that this illufipn an'fcs
from the fituation of the light; and in fail I have
obferved, (fays M. Guypt, from whom this ar-*
tide is taken) that when I have viewed it with a
czndh pp fhe right, it has app^ar^d engraved, but
9^ ^y
29 RATIONAL-
RECREATION V.
T/ie camera obfcura^ or dark chamber.
'\\T E ^^ li^re give a fhort defcriptioa
of this optical invention ; for tho'
it is very common, it is alfo very pleafing,
and though ahnoft every one has feeu it|
^very one knowa not how to conftru(St it,
by changing the light to the left fide, it has iip-»
mediately appeared in relief. It ftill, however, re-
mains to be explained, why we fee it alternately
bellow and promiiient, without changing cither
the fituation or . the light. Perhaps it is in , th^
fight itfelf that we muft look for the caufe of this
phenomenon \ and this feems the more probable,
as all thefe appearafices are not difcernable by all
perfons.
A phenomenon like this will appear to a fuper-
ficial obferver a* very trifling matter: but the phi-
lofopher, who is defirous of explaining all the ap*
pearances of nature, will find it attended with
no trifling difficulties. If is, moreover, by in-f
Vcfl^igating the caufes of phenomena fcemingly in-
fignificant, that the mod important dlfcoveries are
fpn^etimes mad^.
Make
R.£CREAtlONS. ±t
Make a circular hole in the fhutter of a
window, from whence there is a profpe£t
of the fields, or any other obje£t not too
near ; and in this hole place a convex glafs,
either double or fingle^ whofe focus is at
the diftance of five or fi k feet • • Take
care that no light entfer the room but by
this glafs : at a diftarice from it, equal to
that of its focus, place a pafteboard, co-
vered with the whiteft paper f ; let it be
two feet and a half long, and eighteen or
twenty inches high : bend the length of it
inwards, to the form of part of a circle,
whofe diameter is equal to double the fo*-
Gal diftance of the glafs* Then fix it on
* The diftance fhould not be hCs than three
feet 'y for if it be, the images will be too fixiall; and
thefe will not be fufficient room for the fp^ators
. to ftand conveniently. On the other h^nd the
focus Ihould never be more -than 15 or 20 leet, for
then the images will be obfcure, and the colour-
ing faint. The beft diftance is from 6 to 12
feet. ;
f This paper fliould have a black border, to
prevent any of the fide rays from difturbing the
picture.
C 3 a frame
iz R A T I O N A L
a frame of th€ fapae figure, and put \l otf
a moveable foot^ that it may be eafily fixed
&t that exadt diftance from the glafs whercs^
the objeiSts paint themfelves to the greateft
perfedion. When it is thus placed, all
the objeds that are in the front of the
window will be painted on the paper, ia an
inverted pofition ^^ with the grealcft regu-
larity and in the moft natural colours,^^ '
If you place a moveable mirror without
the window, by turning it more or kfe^
* This inverted pofition of the images may be
deemed ah imperfe6lion, but it is eafily reme-
died : for if' you ftand above the board on whicb
they are received, and look down on it, they
-will appear in their natural pofition: or if you
fland before it, and placing a common mirror againft
your breaft in an obhquc direction, look down
in iti- you will there fee the images ereft, and they
will receive an additional luftre from the refleftron
of the glafs; or place two Jenfes, in a tube that
draws out J or^ laftly, if you place a large concave
mirror tt a proper diftance before the pifture, it
will appear before the mirror, in the air, and in an
crcil: pofrtion^
you
R^EGREATIokS. 23
yim trill have on the paj>er stll theobjedis
that are oa each fide of the wmdcm ♦•
If inftead of placing the mirror without
the window you place it in the room, and
above the hole (which muft then be made
near the top of the fliutter), you may re-
ceive the rcprcfentation on a paper placed
horizontally on a table ; and draw, at your
lerfuf6, all the obje£ls that are there
painted.
Nothing can be more pleafing than this
Recreation, efpecially when the objedls
arq ftrongly enlightened by the fun : and
* There is another method of making the dark
chamber, which is by . a fcioptric ball^ that is, a
ball of wood, through which a hole id made, ia
which hole a lens is fixed : this ball is placed ia
v^ooden frame, in which it turns freely round. The
fram^ is fixed to the hole in the (hutter, and the
ball, by turning about, anfwers, in great part, the
ufe of the mirror on the outfide of the window. If
the hole in the window be no bigger than a pea, the
obiecis will be reprefented without any lens.
C 4 not
24 K^TlOhi A\l4 ■ vf
not only; land, profpeds, but, a Xca-{>ortf
when the water is fomewhat agitated, oR
at the fetting of the fun, prefents a very.
delightful appearance.
Thi8f reprefentation affords the moft
perfeft model for painters, as well for the
• tone of colours, as that degradation of
fhades, occafioned by the interpofition of
the air, which has been fo juftly expreffed
by fome modern painters.
It is neceffary that the paper have a cir-
cular form, for otherwife, when the center
of it was in the focus of the glafs, the two
(ides would be beyond it, and confequent-
ly the images would be confufed. If the
frame were contrived of a fpherical figure,
' and the glafs were in its center, the re-
prefentation would be ftill more accurate.
If the objed without be at the diftance of.
twice the focal length of the glafs, the
image in the room will be of the fame mag-
nitude with the objed.
The
R E (J R E' A T t 6 H^ S; 25
. ■ ■ • ' ' '
Tht 'lights,^ Ihades, aniicoldurs in tKe ca-
mera obftura: appear not only juft, but, by
the itnages beihg reduced to a fmaller
compafs, much ftronger than in nature :
add to this^ that thefe pidures exceed all
others by reprefenting the motion of the
feveral objedis : thus we feq the animals
walk, run, or fly, the clouds float in the
air, the leaves quiver, the waves roll, &c,
and all in flri<fi conformity to the laws of
nature. The beft fituation for a dark
chamber is diredly north, and the beft
time of the day is noon.
RECREATION VI.
Tojhow the Jpots on thefun^s dijkj by its
image in the camera objcura.
Jp.U T the objedl-glafs of a ten or twelve
foot telefcope into the fcioptric ball,
and turn it about till it be jliredly oppo-
6 fite
i8 HAT i ^^ A L :
RECREATION VIIL
T/ie portable camera obfcura.
npHE great pleafure produced by the ca-
mera obfcura in the common form,
has excited feveral to render it more uni-
verfally ufeful by making it portable; eafily
fixed on any fpot, and adapted to every
profped. We fhall not here examine the
merits of the various forts that have been
i^ve^ted, among which there are doubtlefs
feveral highly ingenious ; but content our-
lelves' with defcribing one that may have
fome advantages not to be found in
others^.
Let ABGD (PL III. Fig. 2.) be a frame
of wood, of two feet long and about twen-
ty inches wide ; let its four fides be two
inches and a half thick, and firmly joined
together. In a groove formed In this
♦ This fort of portable camera^ appears to be the
invcmionof M. Guyot.
frame
RECRJEATIrO.N«. 29
frame place a plate of clear glafs, E ♦.
To each of the corners of this fraqiejom
a leg, with a hinge, that it may turn up,
under the table. To the under part of the
frame join four pieces of light wood, as
H, which muft alfo have hinges to fold
up; and obferve that when they are let
down, as in the figure, they muft clofely
join^ by means of hooks, it being quite ne--
ceffary that no light .enter the box f •
To that juft defcribed, there muft be
sodded a fmaller box M, in which muft be
an inclined jnirror N, and in one of it? .
fides a moveable tube O, five or fix
fix inches long. This tube muft be fur-^
nifhed with a convex glafs, the focus of
which, by the reftedion of the mirror,
muft reach the glafs Ein tb? frame,, . .
♦ If the upp^riide of the gl^fs were.cpnvex, it
Wpuld be ftill better,
f The infide of the box maybe lined with black
{r]oth, to make it as dark as poffibie.. ,
There
There mufl: alfo be a coverirtg of Mack
fluff, in form of a tentj to place dver the
top of the fraipie, by means of four little
poles that go into holes in the corrierB of
it. There muft be an opening to this tent
on the fide A B, by a curtain to be drawn
up, and which you are to let down over
you, when you place yourfelf under itj
that no light may pnter. The three other
fides (hould hang down fome inches ove^
the frame.
This camera is, indeed, fomething more
cumberfome than thofe that have been hi^
therto invented ; and yet, if properly made,
it will riot weigh more than twenty to
iive-and-twenty pounds. On the other
hand, it is much "more convenient ; for as
the coloured rays of objefts paint them-
felves on the bottom of the glafs in the
framCj you may draw them without hav-
ing your hand between the rays and their
image.
When
RlitGREATIQN-S. 31
When yaa have placed the frame on a
fpot a little elevated, thjit nothing may in-
tercept the rays from falling on the glafs
in the tube, you fix a fhect of tranfparent
varnifhed paper on the glafs in the frame,
by means of wax at its corners. Then
placing yourfelf under the curtain^ you
trace on the paper all the outlines of the
objeds there reprefented, and if you think
fit, you may alfo mark the extent of the
(hadows. If you want only the outlines,
you may lay a thin plate of glafs on that
in the frame, and trace the ftrokes with a
pencil and carmine. After which you
mull dip a fheet of paper in water, with-
out making it too wet, and fpreading it
lightly over that glafs, you will have, the
impreffion of the defign there drawn.
Note, By each of thefe methods you will
have the obj efts either in their natural po-
fition, or reverfed ; which will be an ad-
vantage when the defign is to be en-
graved, and you would have it then appear
in the natural pofition.
In
32 RATIONAL
In ufing this machine, you fhouldmake
choice of thofe obje<fis on which the fun
then fhines, as the appearance of the fha-
dows adds greatly to the beauty of the de-
fign. There are, however, circumftances
in which it is to be avoided, as when you
would paint a rifing or fetting fun, &c.
RECREATION IX.
T^he magic lantern.
TPHIS very remarkable machine, which
is now known over all the world,
caufed great aftonifhment at its origin.
It is ftill beheld with.pleafing admiration,
and the fpedator very frequently contents
himfelf with wondering at its efFed:s,with-
out endeavouring to inveftigate their caufe.
The invention of this ingenious illufion is
attributed to the celebrated P. Kirker, who
has publifhed, on various fciences, works
equally learned, curious, and entertaining.
The
T i V
3 4or«" Ai^t>-3>r
., „ I. ,,,J 1., rfti.t- r r<*".'»^'-r»l re nt-.".
kE CREATIONS. 33
The defign of this machine is to repre-
lent at large, on a cloth or board, placed
•in the dark, the images of fmall objeds,
painted with tranfparefit colours on plates
tof glafs.
Its conftrudiori is as follows. Let
ABCD (PL III. Fig. 3.) be a tin box, eight
inches high, ten long^ and fix wide (or any-
other fimilar dimeiifions). At the top'muft
be a funnel E, of four inches in diame-
ter, with a cover F, which, at the fame tirne
that it gives a paflage to the fmoke, pre-
vents the light from comipg out of the
boxi
On the fide AC there is a door, by which
is adjufted a concave mirror G, of metal
or tin, and of five inches diameter ; being
part of a fphere whofe diameter is eighteea
inches. This mirror muft be fo difpofed
that it may be pufhed forward or drawn
back by means of the handle H, that enters
Vol. XL D the
34 ft A rra o NfA l.?
the tin tube I^ which is foidetfidto thei
door. ' 1^
In the middle of^the box muft be placed
a low tin lamp K, which is to be more-*
able. It fhould have three or four lights,
that muft be at the height of the focus of
the mirror G.
In the fide BD- and oppofite to. the mir-
ror, there muft be an aperture of three
inches wide and two inches and a half
high, in which is to be fixed a convex
glafs L, of the fame dimenfion ♦, whofe
focus muft be from four inches and a half
to five inches, fo that the lamp may be
♦ I prefer this form for the glafs (fays M, Guyot)
that the |);(2ure thrown upon the cloth mjiy have
the fame form, which is much preferable to a cir-
cular aperture, through which the figures can ne*
vcr be cbmpletely fe^h but when they are at the
center of the glafs. It is furprifing that this im*.
perfe<Siion has been fuffered tg continue fo longj
when it is fo cafily remedied.
placed.
HECR'EAfT^IQNS. 35
plic6d:botli iili itis focus^ and; in that of the
concave mirror^
On the fame fide is to be placed a piec6
of tin M N, of four . inches and a half
{quate, having an opening at the fides of
about four inches and a half high, and a
quarter of an inch wide. Through this
opening or groove are to pafs the glafles,
on which are painted the figures that are
to be feen on the cloth. In this tin piece,
and oppofite to the glafs L, let there be
an aperture of three inches and a quarter
long, and two inches and a quarter high,
to which muft be adjufted a tube O, of the
fame form, and fix inches long. This
tube is to be fixed into the piece MN.
Another tube, fix inches long, and move-
able, mufi enter that juft mentioned, in
which muft be placed two convex lenfes,
P and Q^ that of P may h^ve a fqcus of
about three inches, and thatof Q^which is
to be placed at the extremity of the tube,
one of ten or twelve inches* The diftance
P 2 between
36 RATIONAL
between thefeglaffes is to be regulated 1>y
their foci. Between thefeglaffes there muft:
be placed a pafteboardR, ia which is ana-
perture of an inch wide, and 4-5th8 of aa
inch high- By placing this tube farther
in or out of the other, the images on the
cloth will' appear larger or fmaller^
From what has been faid of the preeed—
ing machines, the conftrudion of this will
be eafily underftood. The foci of the con-
cave mirror, and the lens L, meeting in^
the flame of the lamp, they together throw
a ftrong light on the figures painted oa
the glaffes that pafs through the groove,
M N, and by that means render their co-
lours diftin^ft on the cloth. The rays fron?;
Aofe gkffes paffing through the lens P*\
are eoHeded by the aperture in the pafte-
board R, and conveyed to the lens Q, by
which they are throwa on the cloth.
The lantern being thus adjufted, yon
muft provide plates pf cfear glafs, of twelve
Off
1RLECRE ATTON^^^^ 37
'Or fifteen inches long, and three inches
-wide, which arj? to be placed in thin frames,
Aa^t they may pafs freely through the
groove M N, after being painted in the
mariner we Ihall now defcribe.
Method of fainting the glaJJ'es for the
lantern.
Draw on a paper the fubjeiQ: you ^in^
tend to paint, and fix it at each end te
the glafs. Provide a varnifh with which
you have mixed fome black paint, and
with a fine pencil draw on the other fide
of the glafs, with very light touches,"^ the
4efign drawn on the paper. If^ you are
-defirous of making the painting as perfefl:
as poflSUe, you Ihould draw fom.e of the
outlines in their proper colours, provided
they are the ftrongeft tihts of thofe co-
Jours that are ufed. When the outlines are
jdry> 70^ colour the figures with their pro-
per tints or degradations; and thofe colours
will not peel off, if you temper them with a
D 3 ftron^
38 RATIONAL
ftrong white varnifh *. You are then to
fliade them with black mixed with the
fame varnifh, or with biftre, as you find
convenient. You may alfo leave ftrong
lights in fome parts, without any colours,
in order to produce a more ftriking effect.
Obferve, in particular, not to ufe more
than four or five colours, fuch as blue, red,
green, and yellow. You fliould employ
however a great variety of tints, to give
your painting a more natural air, without
which they will reprefent vulgar objedls,
which are by no means the more pleafing
becaufe they are gawdy.
When the lamp in this lantern is light-p*
ed, and by drawing out the tube to a pro^
per length, the figures painted on thejglafs
?ippcar bright and well defigned, the fpec-r
tator cannot fail of being highly enter-
* All thofc colours that arc not terreftrial, aa
Pruffian blue, carmine, calcined verdigris, &c,
;nay be ufed to advantage, when tempered with a,
proper varn^lh^
taime^
RE CREATIONS. 39
tained by the fucceffion pf natural orgro-
tefque figures that are painted on the
glafles*
This piece of optics may be rendered
much moreamufingi and at the fame time
more marvellous, by preparing figures to
which different natural motions may be
given *, which every one may perform ac-
cording to his own tafte ; either by move-
ments in the figures themfelves, ' or by
painting the fubjedt on two glaflis, and
paffing them at the fame time through
the groove, as will be feen in the next Rei-
creation.
• There arc in the Philofophical: Ei&yi of M.
Mufchenbroek, different niiethoji^of p^fffrming all
thefe various movements, by fome mechanical con-
|;rivances that are not difEcult to execute. '
D 4 RECRE*
40 R A T I O N A l4
RECREATION X.
^0 reprefent a tempejl by the magic iantern^
PROVIDE two plates ofglafs, whofe
frames are fo thin that they may both
pafs freely through the groove M N, at
the fame time (PI. III. Fig. 3.) *
On one of thefe glafles you are jto paint
the appearance of the fea, from the flighteft
agitation to the moft violent commotion.
Reprefcnting from A to B (PL IV. Fig-i.)
a calm, ff cm B to C a fmall agitation, with
fome clouds, and fo on to F and G, which
fhould exhibit a furious ftorm. Obferve,
that thefe repi^fefenfations are riot to bq
dirtind, but ruti Jnto each other, th^t they
may form a natural gradation : remembei^ .
alfo, that great part of the effcdi depends
on the perfedion of the painting, and'the
pidurefque appearance of the defign.
On the other glafs (Figi 2.) you are to
paint veflels of different forms and dimen^
7 iions,
RECREATIONS. 41
^ons, and in different diredions, togctheir
yr'ith the appearance of clouds in tlie tcm-
peftudus partjs. ' .
You are th«tf to pafe thft glafs (Fig. 1.)
ilowly through the gtooire, andt^hen you
coftie to that part Where thie ftorni begins^
you are ^to move the glafe gently up and
idown, which will giyp it the appearance
of a fea that begins to be agitated ; and fo
increafe the motion till you come to the
height of the ftorm. At the fame time
you are to introduce the other glafe with *
jthe fliips, and moving that in like man-
per, you will have a natural reprefenta-
tion of the fea, and of fhipi^ in a calm and
in a ftorm. As you draw the glaffes flow-
ly back, the tempeft will feem to fubfide,
the fky grow clear, and the fhips glide
gently o'ej: the waves.
This effed of the magic lantern muft
certainly afford more pleafilire and fur-
prize, than to fee figures, frequently badly
painted,
42 RATIONAL
painted, appear one after the other in the
midft of a luminous circle, as in a medal ;
whofe form, befides being difguftful, pre-
vents you from feeing any two figures to-
gether, without the head and legs of one
of them being entirely hid : an inconveni-
ence that is avoided by this new method,
even when you make ufe of the common
figures*
By means of two glaffes difpofed in this
manner you may likewife reprefent a battle,
► or fea fight, and numberlefs other fubje£ts,
that every one will contrive according to
his own tafte. They may be alfo made to
reprefent fome remarkable or ludicrous ac-^
tion between different perfons, and many
other amufements that a Ijively imagina-^
tion will eafily fuggeft. The inftance we
here give (fays M. Guyot) being intended
merely as an example, and to fhew that
this machine is capable of producing much
more remarkable effcdts than have beea
hitherto exhibited,
RECRE-
RECREAT IONS. 43
RECREATION XL
^he nebulous magic lantern.
TpHE light of the magic lantern, and
the colour of images, may not only
be painted on a cloth, but alfo reflefted
by a cloud of fmoke.
Provide a box of wood or pafteboard
AB (t'l. IV. Fig. 3O of about four feet
high, and of feven or eight inches fquare
at bottom, but diminifliing as it afcends,
fo that its aperture at top is but fix inches
long, and half an inch wide. At the boC=!
torn of this box there muft be a door that
ihuts quite clofe, by which you are to place
\ti the b6x a chafing-difh with hot coals, on
which is to be thrown incenfe, whole
fmoke goes out in a cloud at the top of the
box. It ia on this cloud that you are to
throw the light that comes out of the
•lantern, and which you bring into a fmaller
^pmpafs by drawing out the moveable
tube.
44 RATIONAL
tube. The common figures will here
ferve. It h remarkable in this reprefen^
tation that the motion of the fmoke does
not at all change the figures, which appear
fo confpicuous that the fpcdtator thinks he
can grafp them with his hand.
. Note, la this experiment fome of the
rays pa,ffing through the fmoke the repre-»
fcntation will be much lefs vivid than 6n
the cloth ; and if care be not taken to re-
duce the light to its fmalleft focus, it will
l>e ftill more imperfe£t.
RECREATION XII.
To produce the appearance of aphantom-^ up-^
on a pedejial placed on th middle ofq
table.
P^NCLOSE.a common fmall magic
lantern in a box A B C D (Plate
IV. Fig. 4.) that is large enough to
contain alfo an inclined mirror M, which
muft be moveable, that it may refleft the
cone
cone cf light thrown on it by the lantern,
in fuch manner that it may pafs out at the
aperture made in the top of the box. There
fhould be a flap with hinges to cover the
opening, that the infide of the box may
not be ieen when the experiment is not.
making. This aperture ihould Kkewife
be oval, and of a iizfe adapted to the cone
o£ light that is to pafs through iu
There muft be hoks made in that part
of the box which is over the lantern, to let
out the fmoke ; and over that part muft be
placed a chafing-difh of an oblong figure,
and large enough to hold feveral lighted
coals *^ .
There muft alfq be a glafs that will a-
feend and defcend at pleafure in the vertical
groove a b. To this* glafs let there be fixed
♦ This chafingdifli may be enclofcd in a paint-
ed tin box of about a foot high, with an aperture
at top fomething like Fig. 3. It fhould ftand on
four fhort feet^ to give room for the finoke of tjie^
iamp to pafs out.
a cord
46 RATIONAL
a cord, that going over a pulley ^, pafle*
out of the box at the fide CD, by which
the glafs may be drawn up, and will do-
fcend by its own weight.
On this glafs may be painted a fpeflire,
or any other more pleafing figure. Ob-
ferve that the figures muft be contra&ed in
drawing, as the cloud of fmoke does not
cut the cone of light at right angles, and
therefore the figures will appear longer
than they do on the glafs.
After you have lighted the lamp in the
lantern, and put the mirror in a proper di-
redion, you place the box or pedeftftl
ABCD on a table, and putting the chafing-
difh in it, throw fome incenfe in powder
on the coals. You then open a trap door,
and let down the glafs flowly; and when
you perceive the fmoke diminifh you draw
up the glafs, that thcv figure may difappear,
and fhut the trap door. This appearance
will occafion no fmall furprize, as the fpec-
tre
RECREATIONS. 47
tre will .feem:to rife gradually out of the
pedeftaUvand on drawing up the glafs will
difappear in an inftant. Obferve, that
when you exhibit this Recreation you muft
put out all the lights in the room; and the
box Ihould be placed on a high table, that
the fpedators may not perceive the aper-
ture by which the light comes out. Tho*
we have mentioned a fmall magic lantern,
yet the whole apparatus may be fo en-
larged, that the phantom may appear of a
formidable fize.
By having glafles properly painted, you
may alfo produce the image of a flower,^
or a card, &c. like one you have burnt,
and caft the alhes into the fire with the
incenfe, and by that means pretend to make
the image rife out of the aflies ; with many
other devices that every one may contrive
of that kind which fhall pleafe him belt.
R E C R E-
4^ R A T I O N A 14
. y.\^ \ i * i M ') A >?
.]R.EGR;EATION XHLi ; ,
' Thi nuigical thioire.
tD V piakijag fome few additions W \bi
iQagu; lantera with the fquare-tuW^
ufed ia the ninth Recfeatibn, vitfious
fcenes, charadera^ and decorationai df a
theatre njay be lively reprefentcd.
I^t. there be 6iade a wooden box ABCD
(Plate IV# Fig. 5.) a foot and a half long^
fifteen inches high, and ten wide. Let^it
be placed on ^ ftand EF^ that muft' gd
round it, and by which it may be fixed
with . two fcrew8 to a table. Place over ■ it
a tin cover, as in the common lantern.
- Mate an opfening in its two narrowieft
fides; in one of which place thetubfe fc[^
.;. ^; .. > "• 1 ;:W
♦ Jjt, 19. quite nfice^ary to make the lanterp ^iichr
larger than Common, that the ohjecSbs painteci pof
the gl'afles, being of a larger fi^e, may be repre-
fentcd with greater precifion, and confeq\iehtly
their feveral characters more ftrongly marked*..
and
RECREATIONS. 49
Sind ia the other the tube I ; let each of
them be fix inches wide, and five inches
high; in each of thefe tubes place another
tbatis moTBable, in order to bring the
gl^flfes, or concave mirror, that are con-
tained in .them, to a proper diftance; as
Will be exjdained hereafter.
In the middle of the bottom of this
bpx place a tin lamp, M/- which muft
h^ moveable in a groove, that it may:
be placed at a proper diftance with regard
to the glafles and mirror : this-lamp fliould
have five or fix lights, each of them about
an inch long. See the Figure.
At the beginning of the tube H, toward
the part N, make an opening of an inch
wide, which muft crofs it laterally : an--
other of three quarters of an inch, that
muft crofs it vertically, and be nearer the
box than the firft ; ajid a third of half an
inch, that muft be before the firft.
' . . The opening made laterally muft have
three or four grooves, the fecond two,^ and
Vol. IL E the
5^ RATIONAL
the third one: that different fubjeds dT
figuies and decorationft may be ps^&d^^
either fideways, afcendidg, or- defcending^-
jb that thricenes^ of a theatre may be"
the m(xc€Xj£tbf imitated^. Sacbfe thefir
grooves bebween two eonvez redanguUr
glaiTes, of fik inches longyv and five indbea-
Klgh, and of aboctttwenty inches^ocus; one-
ef which muft be placed at O, and the other
tfi>ward P. Have another^ tube Q^ of
dbout a foot long^ whkh muft' enters
that marked H^ . and at its outward extre—
ttity plaoe a fens of about fifteen inches
i^us.
There rauft alfo be a third tube R». four
inches long, which i$ to enter- that* rnark-!^
cd I : to the exterior end of this adjjpft a^i
concave mirror^ whofe focus muft be at
feven or eight inches from its: refleSIn^
furface,'
♦ In the deceraliolHy tift clouds and* the pa--
laces of the Gods ihould' defcend | cave^ and itof^
fdrnal pahces Ihould arcend^ cafthty palaces, gaf^
dens, &c. eater at tbc-fid«»«
Thi^
jLXTZ-lVr
: I
r. ZOn / i >1 .).?;l
, '' *
.-•fv':;
■ ^-.-i; I :
*: ./lii.
; -Ji.:f';-.;
l,M' ::z-:
^. ." i .w '
:.: L.:.:
ti:;^:
t:j.
• .' , I :
- . . . • .- - .;■; . - . . .i
<jci:„ua»
. HECREATIONS. 51
This magic lanthorn being thus ^djufi-
led, nothing more is neceflary than to pro^
vide glafles, painted with fuch fubjefts as
jHm would reprefent, according to the
grooves they are to enter* The lamp is
'then to be lighted, and placing a glafs ia
one of the groves, you dr^w out the movc-^ '
^le tubes till the object paints itfelf on a
doth to die moft advantage : by which
•you determine the diftance of the lantern,
and the fize of the image.- You then make
a hole in the partition of that iize, and fix
in it a plate <^ clear glafs, over which you
paile a very thin paper» which miift be
vamiihed, that it may be as tranfparent as
. poffible. g
It is on this paper that are to be exhi*
bitcd the images of all thofe objects, that
by paifing iiiccefiively through the grooves,
are to reprefent a theatric entertainnsient.
This exhibition will be the more agree-
ithle> as the magic lantern being conceal*-
ei behind the partitiont the caufe of tbs^
JS a >Uu(ioa
52 RAT ION A L* '
illufioti cannot by any means be difco*
vcred.
In order to flK)w more clearly in what
manner a fubjed of this; fort fhould be
painted, and the glaffes difpofed, we will
itere make choice of the fiege of Troy for
a theatric fubjeiS:; in which will be found
all the incidents neceffary to the exhibi-
tion of any other fubjc it whatever.
In the firft ad, the theatre may repre-
fent, on one fide the ramparts of Troy,
toward the back part the Grecian camp,
and at a further diftance, the fea and the
ifle of Tcnedos. We will fuppofe the
time to be that when the Greeks feigned
to raife the fiege, and embarked, leaving
' behind them the wooden horfc, in which
were contained the Grecian foldiprs*
* On a glafs, therefore, of the fame width
%with the aperture made in the fide AC of
the box, you are to paint a deep blue cur-
tain.
RECREATIONS. 53
tain, lightly charged with ornaments,
quite tranfparent. This glafs is to be
placed in the firft vertical groove, fo that
by letting it gently down *, its image may
appear to rife in the fame manner as the
curtain of a theatre.
You muft have feveral glaffes of a pro-
per fize to pafs through the horizontal
grooves, and of different lengths accord-
ing to the ex^tent of the fubjedl. You may
paint
On the firft, the walls of Troy.
On the fecond, the Grecian camp.
6n the third, the fea, the ifle of Tfnc-^
dos, and a ferenfe fky.
On the fourth, the Grecian trobps, by
detached figures.
On the fifth, otlier troops, difpofed m
battalions, and placed at 'at diftance.
♦ All the glaffes tljat are to rife and defcend
iniift be bordered with thin pieces of wood, aiifi fo ex-
;«£Hy fill the grooves, that they toay not Aide down
oftbcmfelves.; - • . .. -
E3 Oa
5*- ^«:a¥^ro^i?^5.^
the g}ilis a^rabdes iti thegroohrt di&3ti&
infizfel^ ■■- ■- - '•-- ^^
On d^c&rentht the woodeot horie and.
On the dgbtbi Trojjua JOjien ^nd wd>*t
men. ;ia.->. m>i y : •
Thefe glafles being properly painted %
you place in tKe 'lioHzorttal grooves '^he
fitft, <feb6nd, tli?rd, and fbiirtli/ TKctt
draw irp the curtain, by Icttlftg down -flie
glafe bri which It is painted,' and draw it*
wa7 ^gfefttly the' fourth glafs, and after
that the fecond ; then advance, very gent**
ly, the. fifth, that reprefents the em-^
barkmeii?, 'aii'^' pafs it quite through*
Next pafs, the dppbfite Way; the fixth,
"Which V^pfj^lentg the Grecian fleet. The
obj<s;(*is j^aihted^on the fourth, fifth, and
fiktli quitcr dil^j()pearing, you are to ad-*
vance tne Seventh, on which is painted die
, . ^ ySfi^jQfl^ jc^u procure glaflfes, well paii^ed.
It wqr€^)>etter' to/^pre(ient fome comic , fabjed,
wher^ cbaimon pamtinjis may fuffice. ~
^ woodca
«^4raw the horie into the city. Thj5|-cur^
^withdraw the fcenes of the firft aflis and
^iuuf/m tbe^oiMiM)'<M<^4dl^»^nor<kto-
^fe thp focond.
f* b^l; •;.-.. v.-'.)-,:--'-! •:,,?•>■! '•>i'i;.. ;'l).i"''
., ; Jn th€^jC<pc©a^ ad »My rbf Tfprefentci
ct^eipteriwc p^ cjiT the>?iiy of Tx^ :. on
•«np Jtdftmay be ifeen tpp, voodoo, hxxfii
.a^idin thie back part the ,t^p^,,ojf)]F^la«.
XJbe glaffea ^r thi» a^,iaj7, |jp, j^f^cd.-ifi
•^bc. foUQ\ying.jna»n«r* ,. . . , .:,.% ,
^, .,0p tV^. %|t, may h^ pfljajjcs a^i^d houf^
^fpr€fenfing,tfee infi4^;pf a fiitjr,,^ ,.,.^.;.;
On tbe, fefjond, t^e te|P5]^^^^aili^
Tin the ccmte, with jf <;leaj.^jvigl)^t |}*| ^
jwoodcn .horfe» that tKe. Troians haw
placed near the temple of Pallas-
- 'On the'the thirtl, a ttdcJ^ c^^ifeela,
mitii STiion 3J jfeqir Ivead. 'wtol^e^koing
. T >S
5^ I^^(yil!0;Ni AX
to opeij. t]\^ gat^s^of ithe qity.tO/.the^Gxe--:
cians^.,j,^^..;, K.-.. ,,,,, ^ ■ ... ;-"rr.-: ,■:
On the fourth^j different troops of arm-^
ed Greeks; painted on a long glafs, to'
afford variety. ^ \
On the fifth, feveral troops of Tro-
jans. . .-•;
On.the fix,th, various appearances of
fire and fmoke, fo difpofed, that this gls^fs
being drawn up above the others, the ob-
jejitsjp^jmted on the firft glafs,.may appear
in a, conflagration.
B^fbrS^ you Idf aw lip the curtain ybii
Ihould plate the firft and fecond glaffes'.
You thfen pifs the whole thirid glafs flowly ;
a little after, the fourth, on which ai*e
painted the diffferient bodies of arifted
Greeks, and at' the fame time, from' the-
dppoCiU fide, ^ the fixth glafs, that re-
prefents the Trojan troops; obferving to
move thetti 'floWly both in advancing and
retreating, to imitate a combat *• Then
* He' that rhoVes thie glafles, feeing the effeft
they produce, is the better able to ifeiider the Yej^-
fentationas natural as poffible.
draw
dfaW lipv by degrees jthl^'fiitb', oti' Mich
are painted the fire, flame, and fmoke, fo
that thepateces and houfes painted dri the
firft gJafe> toay appear to' take fifis gra-
dually, and at laft prefent a general cfohfla-
gration. After havirlg reprefented thefe
incidents with the great eft attention, you
let fall the curtain to prepare for the third
In the third acfl may be reprefented the
infide of Priam's palace, wHere is' fSeri an
altar, round which feveral Trojan princeffes
appear, who have fled thither for faifety.
On thp jfirft glafs may be painte4 the
palace, . n'l
Onthefecond, a view of the bapk part
of the palace, with th^ altar. ..-a-
Oi;l^ the third, Priam with. feveral; Tro-
jan men and women. ' » ^^
On the fourth, PyrrhuB,: and: ai troop
of Greeks.
On the fifth, the fame a^flors,, with the
! palace in flames. .
On
58 cJ^(^iTrkOfiS:^5Vi
The two firft glaffes TrWdi' ai^^tx^ be
drawn up, fliould be placed before you
wife the cuJtdil. Tlicii j^ ilii Am! ;
ticxt ttdvttncc the fomiili, iWiWh 'iiemg'
cirawn up, difcovers on the fif& the pa^itoil
xn flames, then drawing up tht? fixth, lc(
^WA thefirfty that the pal we ttf a^ ap*
pear entirely delhx3yed by ^t confiagrii^
4ion»-.:;. v-x?
The fourth a<fl may reprefent the ^-
virons of Troy, with a diftfuxt ftofpt^ of
the fea. The firfi and third giafle$ of the
iirft aft may be here ufed, to which ujay
be Added a third, reprefenting Eneas bear^
tng his father Anchifes, followed by tm
loriiulus, and fdme Trojans^ ^ With i}u8
glafs may be reprefented the fligfct of the
Trojans, and the embarkment of EneaSt
with anc^her glafs, on which are painted
<!ertaiii Veflels. - 4?.^
T^ithisf ad the following fcenes imy :l)e
^ded .The CAve of Mi^ioBy ^tivSchxk
pait.
■jSh€ £^j^^cm\A repi^^at the open
i^.,fiK!itk,^ £«ct fof :i;nei« &Hmg for
^^OnilieA^rgkfe H»ift be painted the
U^ as ia the tenth Recreation, or elfc
the waves ihould be unitated by another
^ais tender tiie frriL
K)n ijie fccoi^ The Trojan flefet.
'dta tnejiiurdi Neptttflie in his car.
^On^ tt* fourth, the palace of JujMtcn
On the fifth, the in^de of the palace ;
t|ie <5od$ aflembJed in council, with Ve*
ius, pbbuiimg leave of J«ipter for Eneas
to land in Italy^
i\&er Widg {Jaoed the firft glafs^ that
feprefeibts a calm Tea, the<:urtain is raifed,
ftud the focond fcene is advanced, whicli
fidntairis the Trcgan ile«:. The firft is
sIm^ brought forward; t<5 rejirefent a vio-
/^W knt
6o R A>T ION A L:^
lent tcmpeftt :then raifing the ifcirdglafs,
Neptune appears, who commandB the
waves to be ftill, which is done by mak-
ing the tempeft fubfide by. degrees. . The
fleet then advances, and paiTes over the
whole theatre : prefently after the fourth
and fifth fccnes defcend, that rcprefent
Olympus, and finifh the exhibition.
Note, We muft here repeat, that if you
would reprefent a fubjedt of this fort to
advantage, it is quite neceflary that the
glafles be well painted : and thofe that are
to be in front, fliould be in ftronger and
more opaque colours, that the images
. of thofe behind may not appear mix-
ed with them, which will be the cafe
if they are all equally tranfparenL
The glafles fhould alfo be of different
lengths, that fome being placed before
the others are drawn away, their ex-
tremities may not be perceived.
The
RECR/E'ATiaN^. 6<
'fThb ki'gcr thefe fubjeiSfcs are reprcfcnt-
ed the better efFe£t they will hscve : the
ftont of the theatre fliould appear to be
about three feet wide : and, as we have
-laid elfewhere, if fome parts of the figures
were moveable it would ilill add to
the variety of the entertainment.
This and moft of the other Recreations
we have here given in the two firft parts
of Optics, appear to have becA invented t)y
M. Guyot, who has taken no fmall. pains
in the improvement of this fort of rescrea-
tions.
■)ii'
» ■ .' . ...»
C A T O P-
6« fci^TIOHAlM
CAT OI^TX rosi ^^
.. • • . 'v i; ■ ■ •■ 'i' 'J ->: ■'■/.
/CATOPTRICS i& that part of oj)]tic»
wluch explains the iM'op^rtip^ of, ref
fleeted light, and particul^ly^. that .wl^cb
is reflcdcd from mirrors*
DEFINITIONS.
1. Every polifhed body that reflets
the rays of light is called i miirror, whe-
ther its furface be plane, fpherical, coni-
cal, cylindric, or of any other form what-
ever. ■■■'•:
2. Of mirr6rs there are threepriiicipaK
ly ufed in optical experiments, which i¥il§
the plane mirror, G H I, (Plate V. Fig. i .)
the fpherical convex mirror, G H I,^^P}a<Sfe
V. Fig. 2,) and the fpherical concave mirfefi^,
OHI,(PfeteV.Fig. 3.) ' I
3. The point K, (Plate V. Fig. 2 afta^^:)
round which the reflcding furf:3fcd o^*^ii
fpherical inirf or :is defcribed, is calk#-it$
centre. The line KH, drawn frojft' ife
center perpendkubr to its two furfaces^
IS the mi& of ;<3ie minfchr, ?^iKi tlie point
H, to which that line is jdrawn> is its yor-^
''-^'41 Tfii '(lii^itce l)elWen the lines AG
9iilBG;^'(?kte V/K^^^ is cairedihc
angle of incidence, arid the difiance be-*
tween B G and C G is the an|;le of teflec-
iSon^
n-:>
A ^ H R f & M S,
I; In ar ptain Mirror.
I. The image DF, (Plate V. Fig. r^
WJiU apptefLrasfan ^b^ivd tbe mii'jrDr, a&
tiiwobjea AC Jw- before' it, :, ';>:
,2. Jfhe, igaagp will ^>|MAr<>oft&e! (fame
%f ,1 an^lHi the iaoie ' pe&tiOQ: m :>th)S ob->
i^ft. ■■;' ■•; ■•^ •■ ■ ■ •■.■..:--■•:;.> -r'-.
3. Every fiich iniH}«*F- vriHji^efflc^t ihf
iiaage of 9^ obje<St ,€>f tt<qi«e ii» owiiTength
^fn^l■^bM;|4t|lf -^^ .;;\- ,!' ,ij-;'- I: ■
/,; 4. ICthe obje^be «aopfH|aebodjri^ aiul
ii|f r»jr^&jj[v0il\ the ;mirFO!« nearly iadirea
lMee»^diece will be onlj one image vifible,^
which
6^ .RATIONAL
which will be rieflecled by the inner furfacd
of the glafs. But
. 5* If the objed be a luminous hody^ and
its rays fall very obliquely on the mirror,
there will appear., to an eye placed in a pro-
per pofition, feveral images ; the firft of
which, refledled from the outer furface of
the glafs, will not be fo bright as the fecond^
refleded from the inner furface. The fol-
lowing images, that are produced by
repeated refledions of the rays between
the two furfaces of the. glafs, will be in
proportion lefs vivid, to the eighth or
tenth, which will b^ fcarce vifible.
II. In a Spherical Convex Mirror.
1. The image DF, (Plate V. Fig. 2.)
will always appear behind it.
2. The image will be in the ikme
pofition as the objeft.
3. It will be lefs than the objedt.
4. It will be curved, but not, as the
mirroir> fpherical.
5. Parallel rays JFalling .on this mirror
will have the focus or inuge at half the
diftaiice
tSftaheb &( the ' benter K;^*fitom tiip niirron
6. In converging ray?/the diAknce of
tW objcd; muft be 'eqtial tx3 half tAe dif-
ttoce of tfre center, to' make the image
appear behirid the mirror.
7? Diverging rays will have their image
at le6 \\im half the diftance of the center.
tf the objeft be placed in the center of the
imrrorj its image will appear at one*eighth
oTthat diftance behind it*
III. In a Spherical Concave Mirror.
I. That point where the image appears
of the fame dimenfions as the objedl, is the
center of that mirror.
2* Parallel rays will have their focus at
one half the diftance of the center.
.3. Converging rayd will form an image
before the mirror.
4. In diverging raye, if the objed be at
lefs than one half the diftance of the cen-
ter, the image will be behind the mirror,
ered, curved, and magnified, as DEF
(PJate V. Fig. 3.) but if the diftance of the
objcdt be greater, the image will be before
Vol. II. F the
66 RATIONAL
the mirror^ inverted and diminifhed, asr
DEF, (Plate V. Fig. 4.)
5. The funs rays falling on a concava
mirror, and being parallel, will be col-
leded in a focus at half the diflance of its
center, where their heat will be augment-
ed in proportion of the furface of the
mirrer to that of the focal fpot.
6. If a luminous body be. placed': ill.
the focus of a concave mirror^ its rays
being refleded in parallel lines, will
ftrongly enlighten a fpace of theftowt di«
menfion with the mirror, at a great diC-
tancc,! If the luminous objed be placed,
nearer than the focus^ its rays will di-
verge, and cpnfequently enlighten a lar--
ger fpace *.
IV. In all plane and fpherica^mirrors'the^
angle of incidence is equal to the angle oP"
refleftiont^.
* It is on this.priiicipje that reverberators ar^
conflru£led.
t. This aphorifm holds true of cylindric mirrors '.
alfo, but not of thofe whofe furfaces are. eliptueal«^
paraboIiQ, &c.
RECR.E-
.) * /
ai
t 66t,
J'nr'fU'.
*f IIFW
Bjfta&fYr
>5^./.
.' JJC0^Jim^\
I
I
1
V-\ V
i/'f
.qoy^-' <\v ii
■-. •'' ?o
kECREATIONS. t-j
RECREATION XIV;
Hhe boundlefs gallery i.
jnONSf Rtrcr a box Ab, (Pkte VI.
Fig; I.) of about a foot long, eight
inches wide, and fix high ; or what other
dimenfioa you fliall think fit, provided it
does not greatly vary from thefe proportions*
On the irifide of ttiis fcox, and againft
edch of Its bppofite ends A and B, place a
mirror of the farhe fize. Take off the
ijuicklilver from the mirror that you place
at B, for about an inch and an half, at the
pkrt C, where you are to iiiafee a hole in
the box of the fame fize, by which you
Inay-eafily view its infide. Cover the top
of the box with a frame, in which muft
be pkced a trahfparent glafs, covered with
gauze, oh the fide next the inner part of
the bo3t. Let there be two grooves at the
parts E and F to receive the two painted
fccnes hereafter mentioned.' On two pieces
F2 Qf
68 RATIONAL
of cut pafteboard let there be (kilfully paint-
ed, on. both fides (fee Fig. 2. and 3.) any
fubjedl you thint proper ; as'^ woods, gar-
dens, bowers, colonades, &c, and on two*
other ps^fteboards, the fame fubjedls on one
fide only ; obferving that there ought to be-
on one of them fome objedl relative to the .
fubjed placed at A, that the mirror placed^
at D may not refledt the hole at C on the,
oppofite fide.
Place the two boards palhtedT on hofht,,^
fides (Fig. 4. and 5.) in the grooves TS^,
and F; and thofe that are painted, on one
fide only, ' againft the oppofite mirrors G^
and D ; and then cover the box with it$»,
tranfparent top. This box Ihould be plac-*
ed in a ftrong light to have a good cffeQu
. "When the eye is placed at C, and views:.
the objeds on the infide of the box, o£.
which foirie, as we have faid, are painted^
on both fides, they are fucceflively reflect-
from one mirror to the other; and if,.
HECHE ATI ON S. 69
ifor example, the painting confifts of trees,
they will appear like a very long vifta> of
which the eye caiinot difcern the end : for
*cach of the mirrors repeating the objefts,
continually more faintly, contribute great-
Ij to augment the iUufion.
RECREATION XV.
T/ie/bur magical mirrors^
nrAKE a fquareboxABCD, (Plate VI.
Fig. 4.) of about fix inches long, and
twelve high * ; cover the infide of it with
four plane mirrors, which muft be placed
perpendicular to the bottom of the box
€HFD.
Place certain objedlsin relief on the bot-
tom of this box ; fuppofe, for example, a
piece of fortification, (as Fig. 5.) with
tents, foldiers, &c. or any other fubjed
* We do not mean to limit th^ box to this
fize ; any other may be ufed, provkled, however,
that it' have nearly the fame proportions.
F 3 that
yo RATIONAL
that you judge will produce an agreeable
(fSeSt by its difpofition, when repeatedly
reflcdcd by the mirrors,
On the top of this bo35 pljce a frame of
glafs, in form of the bottom part of a pyr-
ramid, whofe bafe AGFB, is equal tq
the fi^e pf the box : its top I L M ISI, muft
form a fquare of fix inches, and fliould
not be more th4n four or five inches higher
than the boxj Cover the four fides of
this frame with a gauze, that the infide
may not be vifible but at the top I LMN,
which fhould be covered with a tranfpa-
f ent glafs.
When you look into this box through
the glafs ILMN, the mirrors that are
diametrically oppofite each other, mu-
tually reflecting the figures pnclofed, the
eye beholds a boundlefs extent, complete-
ly covered with thefe objecls ; and if they
are properly difpofcd, as in the example
here givenj in Fig. 5, the illufion will
occafiou
rt7o-
J ^ -< '.'
{■ i
FLAti.<VJ.
f}'<e^.f fiS?
j'l^jffjvi^-
1
';*■ ''i
RECREATIONS. 71
t)Ccafion nofmall furprize, and afFord great
tntertainment.
Note, The nearer the opening ILMN
Js to the top of the box, the greater will
be the apparent extent of the fubje£t.
The fame will happen if the four mirrors
placed on the fides of the box be more
elevated. The objects, by either of thefe
difpofitions, will appear to be repeated
nine, twenty-five, forty-nine times, &c.
by- taking always the fquare of the odd
numbers of the arithmfetic progreflion 3,
5> 7> 9> &c. as is very eafy to con-
ceive, if we remember that the fubjedl;
•enclofed in the box is always in th6 cen-
ter of a fquare, compofed of feveral others,
equal to that which forms the bottom of
the box.
Other pieces of the fame kind (that Is
viewed from above) may be contrived,
in which mirrors may be placed perpen-
dicular on a triangular, pentagon, or
F 4 Kexagon,i
72 E.;A T I O N A L i
hexagoaj(that is, a three, 6vc,oribc-fided)!'^4
plane. AU 'thcfe different difpofitions,
properly direfted. as well with regard to .
the choice a» pofition of the objcdtp, will
conftantly produce very remarkable and
jpleafirig illufionsr
If inftead ' of placing the mirrors per*
pendicular, they 'were to incline equally,
. fo as to form part of a reverfed pyramid,
the fubjedl placed in the box would then
Jiave the appearance of a very exteu-
five globular or many-fided figure.
RECREATION XVI,
The enchanted palace.
S \ ' ■ ■
% ■ ■"
/^ N the hexagonal or fix-fided plane
ABCD EF (PI. VII, Fig. I .) draw fix
femi-diameters G A, G B, G C, G D, G E,
G F, and on each of thefe place perpend;^
cularl^, two plane mirrors, which muft' '
join
Rf C|lE^T|aNf. 73
jc^ exidly at the .center G :*, \ ^gcorate
the exterior boundjuy of ^tl^s pierie (yhicji^
i^ at the extremity Q^f the ra !^^k^
texagon) wit^ fix cp,lumixs^ tjlp^t af tj^
fimje time ferye to fqpjport tjl?e j^kror^^ hj
^grooves formed on fhelr inner fides, ($ee
the pf ofile, Fig* i*) Add to thefe columas
thei^ l^ntablaturesj apd pcjyer f^e ^dl^p^ i^
fuch manner as you fliall thin^ Pf pP^^*
In each one qf tl^efp ft^t triangular
fpaces, contained betiveen two mirfors,
place little figvires of p^ftebo^fd, in ^felief,
reprefenting fuch objed^s ag. when feep \ti^
an hexagonal forpj^ \7iU produce an agree-
able efFe<a, To thefe ^dd fn^all ^g^Jf^ of
enamel j; and ^ake particular caice tg con««.
ceal, by fome objed that has relation to
the fubjed:, the place where the niirrors
join, which, as we have faid before, all
jnect in the common center G. ^^ ^ •
♦ Thefe mirrors, placed back to bkcflt, nr/Jlft ber
9s thin as poi&ble^ i . /.
When
74 k A TldN A L
' When you look into any one of tlie
fix openings 6f this magical palace, the
dbjeds there contained being repeated fix
ftines, wTn feem entirely to fill up the
Whole of the building. This illufion will
appear very remarkable ; efpecially if the
objedls made choice of are properly adapt-
ed to the efFed that is to be produced by
the imrrers.
Note, If you place "between two of thefe
mirrors part of a fortification, as a curtain
and two demibaftjons, you will fee an en-
tire citadel, with its fixbaftions* Or if you
place part of a ball-room, ornamented with
chandeliers and figures in enamel, all thofe
objedls being here multiplied will aflFord t
yeiy pleafing profpeQ:.
*RECRE-
flEjCREATIONS, 75
RECREATION XVH.
^0 draw an irregular Jigure^ "which Jhall
appear regular when viewed in a plane
mirror.
PJIVIDE the fquare A BCD (Pi. VIL
Fig. 2.) into fuch number of leflfer
fquares as you fliall think proper, and then
draw on it the fubje£t you would repre-
fent. Make the line GF (Fig. 3.) equal to
a fide of the fcjuarc A B C D ; and after
having divided it into two equal parts at
the point E, through that point draw the
indefinite line AB, which muft cut the
line G F at right angles. Take any two
points in the line A B, as A and B, equally
diftant from the point E, and draw from
the poiiit A the lines AC and AD, which
you muft continue till they meet the line
C D, parallel to Q F.
On the point A draw A H perpendicu-
lar to A B, and of an equal Ipngth with the
lina
75 RATION AL
Sine CD, that is, double of that whidi
formr^ fide of th£ f^uare ABCDJ
^phdAe Ae line C D into as mitny equal
.parts as^ there are in a fide of the fquare
A BCD, and from the point A draw the
lines .A a^ A k From the point of view
Hi df aw the line H D, which by cutting
the lines A ^, A B, A ^ will fhow you the
points of the feftion from which you arc
to drax*- the linesy* £■, parallel to G F and
CD,
Then tranfpofe on the trapezium, or ,
irregular four-fided figure, GFCD (which
wilt be divided into as many perfpedive
fquare^ as there are natural fquares ia
Fig]' I. A BCD) the de%n traced on that
fqifare; and on the line FG, place per-
pendicularly a mirror of an equal fize with
that fquare. The diftorted figure traced
on the trapezium" GCFD being then Viewed
in the^ inirror frorn a point elevated per-
pendicularly over the point B, to the height
of
R EQUE A T I aN S. 77
©f CD, vnW appear exadly fimilar to that
traced on .the fquare A£ G D« It will ap-^
pear equally regular if the mirror be taken>
away, and it be viewed from the point H.
•
Note, Before you colour the diftorted
figure drawn on ^he trapezium^ you fhould
pafte,it on a board of a parallelogram fi-
gpre> whofe fides are equal to the line$J
EB and CD ; and fill up the fpaee beyond
tiie trapezium>with fuch figures as ypui'
ihall think proper, the better to dif-
guife it : thefe extra figures will not ap-^
pear in the mirror, if you have tlj.ev.[xre—
^ caution tp raife at the point B a (land, thaC:
fliall bear a circle with a fmall hole,^thro'
which the objed is to be feen in the mir-
ror. This contrivance will confiderabljr
augment the illufion.
RECR'E*
^» RATIONAL
RECREATION XVIIL
^he magical dial.
pROCURE adiaUafe as ABCD (Pf
VIL Fig. 4.) of the fize of thofe tha^
ar? commonly ufed to hold a watch. Let
It be placed on a pedeftal CDEF, in which'
there muft be a fmall df awef , that can hold
the plate ABCD, (Fig. 5.) on which plate
draw the circle of hours E, and in the
center let there be a magrietic needley
placed on the point of an axis, which,
paffing through the plate, carries on its
othef point an artificial magnet, that mufL
be concealed in the part under the
plate '
*•
Place at the bottom of the dial cafe, At
the part F, another dial, the hours of
* The magnetic needle itfelf may do, if it btf
not too far from the other dial. That this needfc
may not be fufpeded of having b^en touched it
may be gUt, fo sis to appear like brafs.
whicb
,,1 A A y I '^ /: A
\
•i ,17 ^
■ '.f'"^ (■•
-ax;
/« "■ /.'
' ':: '.■'; r.-
•:} U. •■•.>;>i'^-
.■V::;; ^7 ^'^'j
J'W7V'
\
..;■-• 3ci .. :.
VOI^ff.
}
RECREATIONS- 79?
which are to be reverfed, as is expreflecL
raiFrg.6. and whofe hour of twelve muft
he placed next the front of the cafe E*
Adjuft a pivot to the center of this plate^
and fix on it a. magnetic needle.
Cbvcr the openings at the fides of the.
fiont of the dial-cafe (except v^rhere the diali
appears) with a glafs, lined with gauze on
theinfide, that the light may pafs in and
illumine the dial that is there placed.
Toward the top of the dial-cafe place an.
inclined mirror LM, which by refledtihg^
the dial placed at the bottom of the cafe,
will make it vifible at the part N, where
you muft adjuft a circle of pafteboard, that:
bordering the part where the dial appears>,
and being placed on the infide, will pre-
vent the. borders or the back part of the,
mirror from, being feen.
Matters being thus adjtjifted, when the
hand of the dial (Fig. 5.) is fet to any hour,
and it is placed in the drawer, fo that the
hour'
hoof of tWclve may ber nixt the ring hf
which it is pulled o^t, thii band <^.th€!^
other dralri^aiied at the botf(>m of the
cafe, vfHW diredl itfelf to the fame h6ur,
and by looking at the. part N, you
will fee, by the reflection of the mirror,
the hour af)*pear in th6 front of the dial
plate.
Give the dxial (Fig; 5.) to mf oiie, and
tell him to fet the hand, privately, to any
hour he pleafe; and then place it in the
drawer, only obferving that the hour of
twelve be next the ring, and he will then
fee that the hand of the dial at top will
dire<S itfelf to the fame hour»
Note, If attention be bad to place the*
diaWcafe fo on, the table, that the hand of
the dial which is concealed (and which
will of itfelf turn toward the north, when
the other dial is not under it) dired itfelf
to the prefent hour ^heft the experiment i»
making, it will appear the miore extraor-
.6 , .nary;
aginary ; becaufe, ^Cl^ the drawer is taken
awajy it will again turn t j*^ prefent hour»
which will render the caufe of the illufion
ftill mon myfterious.
RECREATION XIX.
^he box of divination.
T ET a box be made with hinges, like
^^ ABtTB (PL Vffl. Rg. I.) of about
eight inches long, two wide, and^half an
inch thick ; divide the infide of it into
four equal parts, by finall partitions.
Have four fmall cafes E, F, G, H, which
• will each of them fit any of the divifibris,
and in each of them you mull fix a fmall
artificial magnet, whofe poles are to be
; placed aa is expreflcd in the figure. ' Co-
ver thefe cafes with pafteboard or very thin
ivdry, on which you are to write any four
figures you fliall think fit.
To a table I L, whofe wood is not too
thicki fit a^rawer, at the bottom of which
Vol, IL G muft
82 ^ AT IP N Ah
muft be placed an inclified mirror. M N, of
the fame length and breadth with the box
juft mentioned. Under the 9pard. that
forms the top of the table, a;ad toward ,the
fide where the drawer opens, place a fmall
brafs rod, turned up at jts extremities, and
on which there muft be four pivots, at the
fame diftance from each other as are the
centers of the cafes placed in the, box.
Thefe pivots are to fupport four cirqles of
pafteboard P Qj^S (Fig. 2, and 3.) which
muft each of them have ^ magaetiQ
needle.
Obferve, that the figures on the pafte-^
board muft not only be reyerfed, but i^uft
be wrote on the under fide, next the bot-
tom of the drawers, that when it is openecj
they may, be feen in the mirror there
placed. Have regard alfo to the difpoli-r
tion of the poles of the needles, in thp
manner as is clearly exprefled in the third
figure.
7
Matters
RECREATIONS. 83
Mattdrs beitfg thuis prepared, when you
iiive placed on the table the box and the
four niahiber^ tliere included, fo that they
may be exadtly over the four circles of
pafteboard concealed in the drawer, that
is, that the cetftdrs of the one may be pre- /
rifely oyer the centers of the other, the nee-
dles on the ckcles will conform themfelves
exaftly to the ms^ets in the cafes; fo
that, if an irift^nt after having placed the
box, you open the drawer fo far as to fee
the mirror, you will there perceive the
number that thjc four figures on the cafes
make.
Then give the box and the four cafes t<J
^ny one, and tell him to form privately
anj number, by placing the cafes in what
order he fhall think fit, and return you thfe
J)ox firmly clofed. You tljen place it on the
table over the circles, and opening the
drawer, under pretence of taking out an
opera glafs, you call your eye on the mir-
ror, and obferve the order of the figures
Q 2
84 RATIONAL
there expreffed. You then fhut the drawcF^
and retiring to a diflance, pretend to dif^
cern, by the opera gjafs, the number you .
have obferved.
, RECREATION XX,
The magical perjpeflives.
AT the bottom of an heptagonal or fe«r
yen-fided box, as ABC D E F O
(PI. VIII. Fig. 4.) of about eight inches
diameter, and an inch' and a half deep %
Place a circle of pafteboard, of five inches
and a half diaipeter, very light, and move^
able, on a pivot fixed in the center H : on
this circle fix a ftrongly magnetic needle I,
and divide the circle into 2 1 equal parts,
as is expreffed in Fig. 7. The top of the
box^ is to be covered with glafs, over which
you rouft pafte a iheet of very fine paper,
paint^ed the fame colour with the box, and
♦ This box fhould be fo conftrudlcd as to ap-»
pear to ' be the pcdeftal to the three pcrfpcaive^
l^ereafter dcfcrlbedj
R £ C R E A 1 1 d 1^ S. 85
^fnifhcd, that the light may eafily pafs
thrbtigh it, and illumine the obje£ts ^vhich
are to be wrote or patinted on the palle-
board circle. Oil the middle of the top
of this box erfcdt a column I, (fee Fig. 5.)
fupported on a pedeftal M, and crowned
with its capital N*
In the gkfs that cov6rs the box there!
muft be three circular holesi at equal dif-i
tances from each other, as O, P, Q^each
of them three fourths of an inch in dia-
nxeter, and on each mull be fixed, im-
moveable, a perfpedive glafs, like that in
the fixth figure of this plate^
CdnJiruSlion offheperfpeSihegldfs.
Provide a ftand of wood A (Fig. 6.) itt
Ifvhich a hole is made from top to bottom,
. of 3--4ths of an inch in diameter ; on this
ftand place the perfpe£tiv6 B C, which
muft have a feebnd tube D, like the com-
mon glafles. In the larg^er part of it F,
G 3 there
86 RATIONAL
there muft be a fmall oval mirror Ej which
inclines or is elevated as. the tube B. i^
thruft in or drawn out. Let there be a cir-
cular hole at that paft of the, tube which
refts on the ftand A, that when the mirror
is inclined, you may fee through the ftand
of the perfpedtive any objcii: that &aU be
placed in the box, under one of the hoies^
O FQ^. Let 'the threiei perfpeaivefc* fa
conftruded be placed> immoveablej oven
thofe three holes ♦
T/te combination of ohjeBs that may he
drawn on the moveable circle in the box. .
This circle is to be divided, as we have
faid, into 21 equal parts, and each of thefe
divifions muft appear under each of the
openings 0, P, Q^as the circle turns round
bn its pivot,
♦ At the bottom of the ftand of each perfpefliVd
there may be placed a lens of five or fix inches ia
diameter, to magnify the objcS.
Yott
Plate.\to.
P CD
>^'4 7*^4 Aij 1.^^ ^/ȣfer
Fi^.S./i35.
m/'^Af^JcJ*^ ■
RECREATIONS. 87
You are tci determine what ttree obje&s
yoii^ would have appear uhder the three
perfpedives ; and fuppofirig, for example,
that they are reprefented by the numeral
figures 1,2', and 3, you will find that thefe
three figures will admit of fix combinations
or different difpofitions, as
1,2,3. 1,3,2. 2,1,3. 2»3»^- 3>^2- 3>25^*-
Then place the numbers, or the objeds
they repreferit, in fiich order that the fir ft
number, i, of the firft combination i, 2,3^,
may be in the firft divifion A, of the circle^
(fee Fig. 7.) the fecond number, 2, in the
eighth, and the third number, 3, in- the
fifteenth divifion : that the firft number,
I, of the fecond combination, may be
placed in the fecond divifion B; the fe-
cond number, 3, in the ninth divifion ; and
the third number, 2, in the fixteenth divi-
fion, &c. Having'thus filled up eighteen of
the divifions with the fix combinations
of numbers, the other three are to be left
blank.
* Sec vol. I. page 9, aphorifm 16-
G 4 The
88 RATIONAL
The circle being thus prepared, is ta her
placed on its pivot, and to one of the feven
fides of the box (Fig. 4.} is to be adjufted
a lever or flop, that being let down on
the circle, at pleafure> may prevent it from
turnings,
Whcp the three perfpedEIves arq placed
on the box, and turned toward the col^mi;^
erefted on.its center, if the.frnalleft tub^
be thruft in, it raifes the mirror that is conr
tained in each of them, a^d by the hole
B the column is feen. If on the contrary
the fmall tube be drawn a little way put,,
the mirror becomes inclined, and you then
fee one of the three objeds that are placed
in the box, under each opening in the
ftands of the perfpedive, and thefe ohje^s
will neceflarily appear in the order pf one
of the fix combinations of which they ar^
alone fufceptible. ^
By placing the box on the table,
in which a magnetic bar, fix inches
long>
R E C RE A f I O N S.-' %
loftg ♦j lAUft be toncealed^and 'vi^iiofe di-
redlfbri you ^now, you iiiay eaflly make
the tlrfe^^ obje<9:s abovementioncd appear
oppofitethe three holea O, P, Q^ with all
their changes; for nothing more is iiecejf-
(ary than to place the box according to a
mark that is on the table, oppofite to which
you are to place one of its feven fides ;
and by letting down the private check you
keep the circle fixed*
The amufements that are to be made
with thefe perlpedives may be varied ac-
cording to the number of different objefts
that can be placed on the moveable circle.
We fhall content ourfelves here with giv-
ing an example in numbers, which may
be applied to any other fubjeft, the dif-
ference of objeds making riot the leaft dif-
ference in the maiftier of performing this
Recreation ; which, when well executed,
* This bar (hould be ftrongly impregnated, that
it maj^ readily tura the pafleboard circle.
never
90 R AT icy I^ A I/'
never fails to excite tKe Hlglieft'adihiratibrtl
Firft then, yon are^fiytb^pfic^tJitfiiloTtt--
able circle, that tfi6 tKtec drvifibns oil
which thete is ndthirig 'wrote may- ^ppikt
under the three hokis O, P, QJ^, and the
fmall tube of the perfpedives is to be
fo difpofed that the mirfots on the irifidc
may incline to forty-five' degreed f , affdrd*
Hefl: the objeds placed under thofeholeis. The
perfpedives being thus difpofed, they are
placed on the tablt, a:nd liberty is given
thofe that defife it,' to loot into theltn, a»
they can then fee no obje6t. Youarfe theii
to prefent to three different perfbns, three
fiich objeds as you IhaH think pYopfef'lj:;
* This muft be done privately, hy mwns of
the check, before the machine is brottght to the
table.
+ That is, behalf way between a line ^rawn
perpendicular to the ground; and its furface. '
% Thefe objefts may be either numbers,^ flowers,
cards, mottos, &c. it is only neceflfary that the cir-
cle be properly painted. You may alfo bave dif*-
ferent circles to vary the Recreation yet farther,
by privately changing them.
we
REdfiLfiATIONS. 9t
^ftt • will fiippofe Here the thrtt num-^
feeirs I, 2, 3* When ea^h of the three
Jperfdns has made choice of crre of thefe
lumbers, you roH the three cards on wHicli
tiiey are wrote^ altogether^ and- put theitt
into the column, oppofite to which the
three perfpedives are placed; and give
each perfonliberty to chtiofeiii which ^lafs
he will feehis objed *i . * '
When the-^ three parties Have chofe
their perfpeQives, the box is* to Replaced
on the table, where the bar is concealed,
faking 'due care to f6t it in fuch dirediooi
that the' openings O, P^ Qv may corre-
fpond to^tjiofe parti of the circle on whicfc/
the objeds are wirote; A fhbrt time'mu;^
I be given the circle to fettle,' and then the'
* It is immaterial which glafs the firft perfoa
choofes, before the box is placed on the table, b^t
if the fecond (hould not nailie that under which his
objedl is placed, the box muft be moved ; however,
is is an equal chance but hedoes^ and in that cafe
they may all three fee their objefts at the fame
time, '
check
pz ;R A ttOU At
check muft be privately let down^ Thd
three perfons then looking through thef
perfpedive l;heyhave each of them chofe^
their objedtswill naturally appear tothemr
in that part of the column where their
cards were placed ♦.
Note^ It requires fome memoi^ to per-
form this Recreation with facility, as you
muft keep in mind the fix changes of or-'
dcr, which the liberty you give the fpec-
tators to fee through which of the glafies
they pleafe, requires. You may, however,
to avoid charging your memory^ trace on
the box certain figns, which at the fame,
time that they appear to be ornaments,-
may fhow you in what direftion the box
is to be placed* ' ■
♦ You may thjcn propafc ta each of them to'
fnake'him fee his objed through another perfpec*
tive, which yon do by removing thq checlc, and
putting the box in a different direction.
RECRE-
flECJREAT!l70K». 93
RECREATION XXI.
TBe penetrflting perfpeStive.
'VlirrC'i^^ the cafe A BCD, (Plate X.
Fig. I.) place four mirrors, 0,P,
Q^ ^» ^^ difpofed that they may each of
them make ah angle of forty-five degrees,
that is, that they maybe halfway inclined
from the perpendicular, 21s in the figure,
in each of the two extremities A B, make
a circular overture, in one of which fix the
tube GL, in the other the tube MF, and
obferve that in each of thefe is to be in-
ferted another tube, as H and I *.
Furnifh'the firft of thefe tubes with an
objed-glafs at G, and a concave eye-glafs
at F. You are to obferve, that in regulat-
ing the focus of thefe glafles, with regard
to the length of the tube, you are to fup-
* Thefe four tubes ipuft terminate \t\ the fub-
ilance of the cafe, and not enter the infide, that they
|nay not hinder the efie6t of the mirrors.
^ pofe
94 RAT I MAX.
ppfe It equal to the line O^ or vHual pointed
ray, which enterijig at the overture G, is
refleSed by the four mirrors, and goes
cut at the other overture F^ where the oc-
cular glafs is placed. Put any glafc you
will into the two ends of the moveilbte
tubes H and I ; and laftly place the ina-
chine on a ftand E, moveable at the point;
S, that it may be elevated or depr.efled ^t
pleafure.
When the eye is placed at F, and you^
look through the tube, the rays of light
that proceed from the object T, paffing
through the glafs G, are fucceffiyely . re-?
fledled by the mirrors, O, P, Q^ and R,
to the eye at F, and there paint the obje£|:
T, in its proper ^fituation, and thefe ray^
appear to proceed diredly from that obij
The two moveable tubes H and I, at the
extremities of each of which a glafs is
placed, ferye only the more to difguife the
illufipn.
illufion; for they have no copimuni-
cation lyith tjie interior part pf tfoe ma-^
cj^ne. Xhis ix^yin^fit Ijeipg moveable
on the ftand E, may be direfted to any
obied:; and if furniflied with proper
glafles w^U ^nfwer ,the jpurpofe of a com-p
mon perfpedive.
The two moveable tubes H and I being
brought tpgetber^ the machine is direded
toward any obje.dt, ^^nd defiring ^ perfon
to look in at the end F, you afk him if he
fee diftiu6Hy that bbjedl. You then fepa^
rate the two moveable tubes, and leaving
a fpace between them fufficient to place
your hand, or any other folidbody, you
tell him that the machine has the power
'of making obje<fts vifible through the moft
opaque body j and as a proof you delire
him.then to look at the fameobjed:, when,
to his great furprize, he will fee it as dif-
tinft as wl^en therp was no folid bpdy
placed bctweci^ the ^ubes.
Note,
56 . ;», A,T,.ION AJ.
Note, This Rpcreatiofa if thftHUttejix-
traordinary,^ as it is very^ 4iii^Qi^**o ^^^-
ceivehow tl\e eflFe£t is projiijpcd* >Thc
two arms of the cafe appeaj:i](^g to be lo^de
to fupport the jperipeaiyc ..gl*6j,^^a^
to whatever objed it is ' direfted, the ef-
feft is ftill the fame. . . ;*
RECREATION %Xm^
^\eiridgkiaiis mirrors.
TN. d^epattiUQ^. iS^B, (Plat^X.JRg. ?•)
ipake two oyerfpreis* CPt and >EF> of
a foot high, ^;^iid t?n inq^esiiwide, and a^
bout a foot diftant from wchrotiherr 'JuCt
them be at the cpmmoij height of a man's
bead ; and ia e,ach of thegi pjace a Ikani^
parent glafs, furrounded yriith; ;a 'firiwiic^
li]^:e a common mirror^ , i , .
Behind thijs partition place two mirpora.
H ahdl, inclined to it in an angl^. of
forty-five degrees * : let them be both cijgh-^
jteen inches fquare : let all the fpace bc^
* See page 96.
twees,
tween them be enclofed by boards or pafle-
board, painted black, and well clofed,
that no light may enter : let there be alfo
two curtains to cover them, which maybe
drawn afide at pleafure.
When a perfon looks into one of thefe
fuppofed mirrors, inftead of feeing his
own face, he will perceive the objedt that
is in front of the other ; fo that if two
Vperfons prefent themfelves at the fame
time before thefe mirrors, inftead of each
one feeing himfclf, they will reciprocally
fee each others
Note, There fhould be a fconce with a
candle placed on each fide of the tW6 glaf-
fcs in the wainfcot, to enlighten the faces
of the perfons who look in them, otherwife
this experiment will have no remarkable
cfFea.
This Recreation may be confideraBly
improved by placing the two glafles in the
Vol. II. -H partition^
o8 -k A T I O N A L
iyartition, in adjoining rooms, and a nuni-
ber offterfons beiiig ptevtouuy placed in'ohe i
room,when a ftr^ngfef enters' Ihe other, yoil
may tell hnn his^ce'is dirty, afiS' aelife
hiiri t6 look'in^the gtais, wMclifie wiirna-
turally do; rtnd on ftielng aftfahgeiacc
he will draw l>ack ; btit f etuf ning to it, and
'feeing Another,' ' ano^licr,' attd' 4nottier,^*like
tlie phantom kings' in Matbetli, ^nat fiis
lurpriief will b'd Is 'more ekly '' to conceive'
than exjirefs. . After tnis, a reat mirror
may be privatet/leVdowh on trie pacK of
the glafs, and if he can be prevailed to look
in it Once mor6, Ke Wi}rthen,.t6liis furtT^er
jiftoni{hment,.fee his own face j and maybe
told, perhaps perfuaded, that all \\t thought
he faw before was mere* imagination.
How many tricks lefs artful than'this^
have .palled in former, times fotribrcery j
and pafs at this time^ id foimc oHintrkrs;
for apparitions ? .:\'^;
Note, When a .man looks in a mirror
that is placed perpendicular to another, his
face
RECREATIONS. 99
^ iiPace will . appear entirely deforn^ed. If
' the mirror be a little inclined, {p as to
make an angle, of eighty degrees (that is
one ninth part from the perpendicular) he
WiU'then fee all the parts ofhis face ex-
cept t!ie nofe. and forehead. If it be in-
.'"■>'■" i'^ ■ ■'' ' '■ ■' ' . . ■
clihed to' fixtj "degrees (that i^,,one third
part) he wiJl appear with three npfes and
fix eyes : in Ihort, the appar^ent deformity
'Win Vary at each degree of inclination;
titid 'w^en the glafs comes to forty-five
. degrees^ (that is, half wa,y,d.owh) the face
win Vanifh. If inftead of placing the two
mirrors in this fituation, they are, fo dif-
jpofed that their jundion may be vertical,
th^ir different inclinations will produce o- >
ther effeds; as the fituation of the objed:
relative to tbefe mirrors is quite different.
Thceffeds of thefe mirrors, tho'agh re-
markable enough, occafions but litrie fur-
prize, as there is no method of con-
cealing the caufe by which they are pro-
duced. ^
H2 RECRE-
100 RATIONAL
/
RECREATION XXIIL
Polemofcapes,
tl) Y the term polemofcope is meant any
inftrument, whether catoptric or diop-^
trie, by which yoii may fee what pafles in
another place, without beiag feen from
thence. Thefe machines contain one or more
plane mirrors, which ccxivey by refledicm
the image of the objeft to the eye of the
. fpedlator. There are fmall inftruments of
this kind, made in the form ofanopera-
glafs, by which, while you feem to look
ftrait forward, you fee what pafle's on one
fide, ^nd by that mean gratify your cu-
riofity without the appearance of incivility.
To the conftruSing of this fort of pole-*
mofcope nothing more is neceifary than to
fix in a common opera glafs a fmall mir-
ror, inclined to an a^gle of forty-five de-
grees, and adjuft a proper objed-glafs.
This glafs at the fame time may anfwer
its
RECREATIONS. loi
ats common ufe, by addifag an oBje<3:-
glafs, and fo contriving the fmall tube that
it may reB[iove the mirror ^t pleafure, a$
in the 2 |ft Recreation. *
f.
Thetiibe pf a poiemofcope may h^^plac-
cd againft a Ayajl, the inclined mirror be-
ipg a little above it, and turned outwards,
by which mean you will difcover what
pafles on the other fide, without being
feen yourfeif. An inftrument of this fort
would be of ufe in fieges, where there is
danger without the wall from the fire
of the enemy ; and on other occafions.
This inftrument may be alfo fo conftru(3t-
ed, that the tube may turn round, and the
mirror be elevated or deprefled, that yoa
may fee fucceflSvely and at pleafure,
all the obje<3:s that you would perceive if
you were at the top of the wall againft
vwhich the inftrument is placed.
H % , RECRE^
102 RAT I 0,N.AL- .
' ' -^ * .. i .: I . f
RECREATION ItXjV^
^Tht tnchantid mirror u
M
[AKE a box of wood, of a cubical
of about fifteen inches every way. Lejt it/
be fixed on the pedeftal .P^, at thtj , ufu^], . ;
height of a man's head. In.pa^h^.fidje , of
this box let therf; be an opening pf a^pi pva|
form, of ten inches J:jigh,.»nd feinpn wide^
In this box place two mirjppirs Ai /I)|
with their backs again ft each other j let
them crofs the l)ox in a diagonal linj^, and
in a vertical pofition. Decorate the qpen-^
ings in the fides of this box with four oval
frames and tranfparent glafles, and cover
each of them with a curtain, fo po^Jtrivexl .
that tliey may all draw up tpgetl^fer. ?.
Place four perfons in front of the fouf
fides, and at equal diftances from the"
box, and then draw up the curtains that
they
RECREATIONS. 103
they nD^y^^f^e themfelve?. in the jiyrrors;
when- each of tKem, inftead of his own .
figure, will fee that of the perfon who is .
Iiext him, and who, at the fame lime, will
jfeem to hini to be placed on the oppofite
iide. Their confufion will be the greater,
jas it will be very difficult for thein to dif^
cover the mirrors concealed in the box*
>The reafoh of this phenomenon is'evidentj
for though the rays of light may be turn-
,^d afide by a mirror, yet, as we have be-
fore faid, they a^way§ appear to proj:ee4
in right lines.
RECREATION XXV.
Xhe animated optic balhl
(by ajingje refiedtion.}
npHIS piece of catoptrics, as well as tbj^
which follows of double refle<9:ion,
t)eing of the clafs that produces the moft
pleafing illufion. we fhall here give a fuU^
Retail of the manner' in which it is to be
executed...
JI 4 Provide
Prati^^T ft wodden bpx ABCDj of^a^^
bout ty^bfett high, and fiftcsoDrifiches -
wide ,(PMte IX. Pig. i^ wid toward! the -
top Jet th?r/e be made an opening" EfoB
eight oif Dine inctitis high,, and fcven or
eight . inches. wi(}e, a^nd in this ©pening,
fix a tranfparent : gla& t^* Xet the; box. be
two feet deep (fee the profile A BCD, Fig^
2.) and^adjuft' to 'it a 'partition ST, oi the
fame '^ldth,''atid''te'-is fiten inches
deep fF6fkiS't'6 'f ;^Wefve, "that this pari
titiofj w^l fe^krkii Ihfe 'l)ox into two di-
yifionsi ^ We tppet of which muft be one
or two Indies lefs than the under.
In th^ uppfer divifioh, and toward the
cxtreiiiit^ S of the partition S T, 4nd crofs
it, placbl a fmall decoration K S, of the
figure 6f the outward fcehe of a theatre,
in ^idi' lilt there be an opening of ten
inches wide, and eight inches" high.
f If the ^ibienTions of the box l)c larger, the
fxhibitioioLfViUke tnpre'perfeA ; and on the con-
ffarjr, if^\^fjx\^]hf^ it.jwill be left perfc^ap
--, J, Behind
(Fig?fbi]i ifflan laligki of ^t^-fiw d€jg^
as aol ttlie ixjomnboa optical' ^^alchiniid, ^ and
obferve tljfl^i it?^ of thb' ftme WWtli ^ \^itli
the! 6ox, ^aiidb large . e^odgh to cover the
ovQrtuitecfif thtffront &enei>^wheii' the eye
is f^cedjat «ihe tdani^area^ glaf^ E^ '
Decorate , the interior fpape KSBT,
withfuch dlfi^jsirfnt paitftii^^
judge willrf^.ntribute mpftto the,pleafure
of the e^bition. ; Coyer the tpp of, the
box, from. .|$Lto,35, with a fram^ in which ^
is a glafs lined with gauz,q> that th? light
may enter the part KSBT. This firft
conftrudion being made^ in. the propoijtiona
and with tjxe ,pj:ecautions h?re|laid dpwn, .
^ou are next to place the incline^ planp,
hereafter defcribed, y^hich. . muft be, of a
fize tP ^nter ^his edific? by ,?!» . back 4pQr
made at. Gilt ,r
ConJlruSiion of the inclined plane.
This plane Ihpuld incline to the bafe of •
the ftrudlure in an angle of about thirty
; '^ degrees^
io« NATIONAL
..: '•■. / ■ , ■' • ■ ■ • / ;*'^ / *:!.- •^- '
€kfnfiriiStdn 6ftlie wheel for remount^n^the
^ ^^^' -ialls tn^^^ . ,' .^
. , >■•.••■ • ' • ■
* Iti the; center of the toothed t*^h'efel AV
(Plate IX* Fig. 5.) place a barrel with" k
f|>ring, and let it be alio ia the center of
the brafs rod FGr. The pinion of the ^heel
B is to take the teeth of the firft wheel
A ; andiit^ teeth ard to turn the fly Q wlibfe
wingS) muA: be tooveable^ thatby beinjg
more dnlfafe kidHftcd^ they may ateceleratc
or retard the motion of the machine.
To ,t^p,;9yfae4iA,^-t th^re; be iked twa
brafs rpds*, and at the extremity of each
there ,^ft. be a box D^ (fee the profile Kg^-
6»Plate^X.) whofe ovjerture M N isclofed
by a j|^lye,H, that moves freely on the
j^intl;^ the axisof thi? yalve muftcome
put bcyQ^d the furface of the boxy that
the chcfkL may be there placed, which
* The ^18 of this Whcd fliould projeft, that
i.tim»y he,iw>und li^Jibyt key, lii tht fame inao-
Her as a clock.
> fhould
RECREATIO.N^. 109
fbouldmove freely, and at the fame time
with^ the valve. Thef<? boxcja-joaijil: Jjc larg«
chough to contain, each of A^ra,. one of the
balls, that are, as w6 have faid, to roll on
the inslifled .plane, .(Fig^- zJjyjasi tiih^v it
^xay pijtqr ^.th^ fideM of thQ>valv6y which
muft then clofe. The fides of thefeboxtes
mufl: incline, as in Fig. 5. Plate X.
^ pl^ferye alfo^, tb?.t.tbis. wheel muft be
of aproper fize to place. at the back of this
macjiine^. near that part wiifere-the^ftnclia--
ed plane is placed, {fee Kg* 4«l(late IX»)
that it may not only receive in its revolv-
ing boxes the balk, that after having roll-
ed on the plane, p^ oiit by tK6' groove
P, (Fig. 2.) but may alfd raife tb^em a-
gain to the height C, (Fig. 4.) where thera
fhould be a fmall channel to receive and
conduct them to the top of ther inclined
plane. Remark alfo, that toward the part
M there muft be a little iron catch, that
may fuoccflively ftop the checks L, which
are fixed to the axis of |he valves, that it
niay
•miygrve i'wrid tSS tfecball-topafs' iiittAlife bik
at theJpart ■M>'>«fid ilftfc(arge'tft\S <bhfe<ik'L :
•ia Rke'inahHer #fetri'*h)e'Bd«'iidriies t6"tHe
'hetgitt <df tb* gi^VePtlrtf is W" idiidd ffc- the'
•battt* to<? ih61in<ia)pahe- ^thert 'fii'tiri''tec
another titfck to dp'en the rialve'iirid Wif-
vT ,
The wheel being thits placed, it the
back 6f fefrntecfeirte,-'^A rffe'^fihg wbund
>up,- thfc'biilfe ^v^M^TOBkhay defefep Aa
*emed!lt^t»p3ffit5 ^lrfh|;-tTi \^e bS^^it the
akis-df-the'wKy^i Js'^tc^fttib^t*i" "
the tc^, bfidrufi^a(*wti' tfeeiliGlfneli ^MeV
he thatlck>ks ihtO' the gfefs placed in fraivt
of thebox^ WHl imdgfee thkt*itifce^^ by
vtriottft'tuMlngg, atid'gries but dt the t6p
ofthdvtdifice.' ^The ttjp|)ear2fnce W^
come *He« mofe pieafid^ as the
* .There fhoujd be a cafe over' this wbce), with
a door to open, that the contrivance cnay be <j,uitc
'/ree" fr'oni Jeteflion,
windings
RECREATipMS. i|i
Wmdings of the baU areprojpprty ?(J^ed
to the fuhied paiated pa Jthe. incUne;d
plane. This .f^eof . ,^hfi^ ■ executfld .witfi
fcjire, produces a very remarkable illufion)
and is ope gf, the moft J)leji(ing ^creations
■ RECRE'A.tipl^ XXVI. .
^hefane ixhiiMoh by a douile rejteSHon.
r ^ ' - . ■"■'*!
haying ?. fxi^fpr incjf ned i^ aarangl^
pf forty.-^Ye d^r^es, (ffe.J^late |3f* f ig-- 2i)
in thf room o£ the inclined plapc, and by
bavjftg tb^e pJf^ae pu whiph the. balls roll
Ijlace^.neajf the |piart pf the box TI?-
ST, and in a. pof^ti9^ ^\^9^\iQri^ontii\
little columns, arbours, or otber obje<as,
made of brafs wire, at equal diftances *,
♦ This wire fliould have a fmall inclination,
which maybe two tenths of an inch for ev/ery foot;
V and the diftahce between the wires Qipyjd be.fomC'i
thing 'Jefs than the diameter of the balls,
^ . ' *(. *
and
112 RATIONAL
and joined together at the bottom by fcrtii-
circles, which miift be fo contrived as not
to obftru<a the cotiffe of the ball.
If there be fufiiciefit foom, ytou may
place, under the former, another fange
of wires, that have a fimilar 'difpofitiony
fo that the ball, after having run over the
firft, may defcend to the other^ which
will have a remarkable effed: ; as the balls
will fecm to rencounter and pafs over each
other. There muft then be two conduc-
tors, fo that one ball may enter at one
fide, and the other at the oppofite fide.
There fhould alfo be a third condudor,
which, after the ball has paiTed over the
firft piece, may carry it to the top of the
inclined plane, placed oppofite the fecond
mirror, that it may then pafs through all
its windings.
Note. Thefe exhibitions may be varied
at pleafure, as that depends entirely on
the tafte and invention of thofe that con-
ftrudl
i A 5^ O I T A i! s:tt ,
Platetx.
in itfii^.h:\/»m4Bl^4 flrjin dairitiLigsrnt^
ittu€t tibem. You (hould obferv^ to give
but a iior^r^ finall inelinitkm to die gMoves
ia which the jballs run. Thefe balls maj
be of ivory painted, as thofe of brafs
niake too much noife in the box^ and are
fubjedt ta break the inclined mirror, when
by chance they jump out of the groove
and fall on it«
The grooves fliould be concealed a«
much as pofiible by paintings or orna<»
merits. They fhould be either of braf^
tiiK, or thin pafteboafd. tri a word, too
much care cannot be taken in conducting
exhibitions of this nature*
VoL;tL i kECRE^
114 R>AT I ON A I* ,f
RECREATION XXVII.
To defcrihe on a plain furface an irregular
figure^ nvhich Jhatl appear regular when
placed oppofite a multiplying gtafs^ and
feen by reflexion through an aperture
made in the center of the drawings
'\Kf E fhall not here lay down the geo-
. . metric manner • of drawing thia fi-
gure, for it would notonly be very Gomr
plicate, and extremely difficult to ea^qcute,
but when done cojuld not fucceed, .on fiC-v.
count of the impoflibility of, procuring
glafTes of this fort» whpfe planes are equal-
ly inclined and perfedly regular*
CONSTRUCTION*.
Procure of an able artift a mirror of
metal (Plate X. Fig. 4.) Whofe baft is a
hexagon of about two inches and a half
' in diameter, and about half an inch thick
at its center. Let the faces of this mirror
be very truly cut, their angles very Iharp,
and
RidREAridN's. 115
and their furfaces highly polifhed. Cd-
hient thi^ mirror to a ftatid of about half*^
an inch thick, and let it be firmly joined
by means of a fcrew, at the pbiht A, (Fig*
^.) which fhould be eight or nine inches
high; and let the ftand be folidly fixed od
the top of the box B G*.
^ At^the end G of this box (Fig. ■^!) placeJ*
an upright 'frame with a groove, which is
to remain there, and in which are to bci
{)laced the defigns, of about fifteen inched
fquare, containing the different diftorted
figures that are to appear regular, when
jfeen ia the glafs, which, ad appfcars hf
the figure^ will then be oppofite to iti
In the center of the drawing make a hole
^f ^abQut three tenths of an inch in diatmc-*
ter, thrpugh which the mirror may be en-«
tirely feen, and which ftould be placed
- * This box may have a drawer, to coouia
. the diiFerent paintings that are to be £een by the
xiiirrbr : it may be eight or nine inches wkie» and
fifteen inches deep.
1 2 exadly
ii6 .KJ^Ti ONiAL5i
exa^lji Qppfiilte th»t hole, wkh its Bftfii
parallel tp tUc drarwing or pi^t e« : :: -:
'Drayjr, qa a paper or pailet)pi^t!i«.g;(MH
Tfictxi^ pj?j> of the n>uUipIyi«g :gb&^ (fcc^
Fig. 7.) and oa that draw - tihe 4cfigOL .:j«m
would have feea in the mirror^ Thefe
preparations being made with^^reat attcn-
tioji> th^t i3> th^ mirror Uiftg properly
fiiced, and tjbe. drawing <rlght;Iy :94]U](Mf
Iqok, at the miwor through ^he hol^ J^
made in the draining, andhqldi^g th^oEttklf
AB% by its handle D, (fee. Kg. ,^)t;i«
your left hand, move it in differeat di-»
ledions. oyer the drawing till its. ^6fi G
appear to the eye (remaining; cojjfi^ntly au
H) to be exactly even with one of the
fides of the glafs; there keep it fixed j.
and taking the eye from the hole^ draw
with a, black lead pencil, that yott have
i«ady in the other hand,, a line by the
* THis fiilcr fliould be about three or four
inches long, very thin and black, Tt m^y fee
made ci part of the fpting of a clock.
ruler-
RECtlEATIONS. 117
ciildr. : D© the fame by the other fides of
Ihat face of the glafs^ arid then the fpace
contained between thofe two lines will be
thatrOff wWdfe yoa arft to tranfpofe tha$
part of the defign which is drawn on the
Citufefpottding face in Hg. 4.
• 'D&^tlW fUfae ^ the other faces of
tii6 ^fe^ AAfi T^ ^^^^ ^^^^ ^^^^ twelve
fa^s that will correfpond to thofe of the
iftirror, and which altogether muft confe-
^tiently contain the entire fubjed that is
trace<f on Fig. 7.
- Thefe fpaces not differing much from
thofe of the mirror, it will be 6afy to trad*
t!w obje(9t that has been defigned ; it will
be only tieceflary to number them, to pre-
sent any.miftake; and to place the paper
or pafteboard before the mirror, after you
have lightly traced the defign ; and infpe<3:
it by the hole H> that you may difcover
and rectify any errors that may have been
made. Thefc fpaces may alfo be fubdi-
1 3 vided.
1,8 RATIONAL
Tided) as well on the defign as the diftertw
cfi figure, in the manner expreffed in Fig,
8^ and by th^t means the tranrpofitioa
wil)^ be made with ftill greatfir, facility*
JLaftly, you fhould fill up the vacant;
parts on the pafteboard with figures that
have no analogy with thofe in the original
defign, and by th^t me^qs render it ftiU
lyiore furprifing,
This experiment will pi'oduce a moft
agreeable illufion to thofe who are igrr
norant of the manner in which it is per-
formed : for, when looking at the point
H, they cannot difcover the leaft refem-
blance between what they fee in the mirr
ror, and the general defign on the pafte-^
board.
pbferve, this drawing may alfo be
traced corredly^ enough by' means of
^ lamp, placed at the point of view H,
taking care to enclofe it in a tin cafe, and
tQ
MO J r ^ :f iiOa ::r
a-::.
•'.ir-
'^\ U
UECREATIONS. 119
to adjuft to it a tube of about an inch
in diameter, and three or four inches
long, that can be protracted or fhortened
al: pleafure. When you ufe this method, a
hole mufl: be made in the paper, large e-
nough to admit the end of the tube ; fo
that the light falling on the feveral faces
of the glafs, they may hh refledied on the
paper, and fhow where each of them is
to be traced. By this method the time
fpent in finding them by the ruler is
faved; and if the light be fteady, the
drawing will anfwer very well. You
may alfo draw on the mirror, with foot,
tempered with fme white lead, all the
ilrokes of the defign, and by that means
^ill fhorten the execution of the drawing.
I 4 RECRE-
^29 ^'A>riO^-^U^i
R E q R ]& AT lOij -XXVJJL >
To iejtribi on a plane furface a defarnieJt
figure^ which Jb^l upbear r^'gul^r ^en
viewed by reficBion in ^ cytinthicitkl Jfdry^
npHE geomctriq method of deliiiWhgf
this irregular figure, being, as ih the
lail Recreation, not only extremely dif*
ficult, on account of its different curves,
but alfo liable to error from the want d£
regularity in making the mirrors ; we
ihall iiere fliew another methpd of de-
fcribjhg it, far lefs learned indeed, but
much more concife, and eafily practicable
by thoie who have not a profound know-»
ledge of geometry, but are yet defirous of
drawing; thefe forts of anamorphofes,
Xiet iABCD be the cylindrical mirror *,
(Plate Xlf Fig. i ,) in which you would fee,
• i*|g. 6. Plate XL rcprcfcnts the projeflion
pfkhepjIindricVnlrrQr, drawn on paper.
from the point of view E, the deformed
objeftipaiathd^^ a
regular form.
.■'f'\
On'i papef, or p^board; drawflie
circlfe A^^ (iRgf. 2,) cqfial' to" Sie' Safe B J>
of the cylindric mirror; and taking the
point B for tbe diftanc^ of Ihe ppint of
view from the mirror> draw the line A B,
which mutt pafs through A, the center of
the circle. Then draw the, twp lix^es
BCandBD- : =
Divide the line C D into fix equal parts,
and draw from the poujt of view B, the
Jines B/, which by cutting one of the j^d^s
of the circle, will determine the points on.
which you are to ered: the parallel gerpcn7
diculars, which may be done by a ruler;
making ufe of an opaque colour that will
efFedually obfcure thofe parts qf t^e cy-
linder where they are drawn ♦^ ^ , y^
* You may ufe foot and .i^Jsite ^^d ground ^to-
g^th^r with Kum, after having traced the lines with
S crayon,
' Thefe
122 It A T ION A L /
Thefc firft divificns being regularly-
made, divide about two thirds' Of the height
of the fide CD, of the cylinder,, iftto ten
or twelve parts, refpedively equal to thofe
of the diameter of the circle (Fig. 7.) and
from the point of view E, draw thr! lines
E /, which palling through all the points
of divifion, muft be continued to' the other
fide of the cylinder. On the two oppofite
fide$ of the cylinder piark the different
heights of the feveral divifions, and thro*
thofe points draw the oval figures i/^
jnaking ufe of the fame colour as be-
fore, . ' ' "■■
Take a paper A BCD (Fig. 3.) whofe
two fides A B and C D muft be divided
into fix equal parts, and thofe of AC and
BD into ten or twelve equg.1 parts^ on
whiph you are to draw the figure as you
would have it appear to the eye when
viewed in the cylindric mirror. At the
point of view E, place a lamp, fo difpof-
ed that its light may fall on the cylindric
mirror only.
6 When
RElCREATIONS. 123
Wheft you have fixed the cylinder om .
%ht pafteboatd F G (Fig. 6,) and the lamp
isr placed at E, fo that its light cannot
fkU on the -pafieboard, but by refledtion,
all the ftrokes on, the cylinder will then
appear on the board, and may be eafily
traced with a penciL By this means the
board will be divided into as many irregu-?
Ur fpaces, as there are regular divifions in
tW parallelogram (Fig, 8,) If,, therefore,
you transfer to each of thofe fpaces the
ftrokes of the defign that is on the paralle-r
iogram, it will appear qiiite deformed on
the pafteboard, and quite regular when
feen from the point of view E, efpecially
if due attention be had to drawing the
putlines of the figure.
> Note, The point of view Ihould be four
jor five inches above the upper part of the
mirror, that you may not be obliged to
inake ufe of a very large pafteboard : it
fliould not, however, be much higher, as
then the figure on the board would not be
fufficiently deformed*
By
«?4 .?3-^{^^r9.^^^^<i..
By this method.you may alio draw ir-
regulaj; j^^res ^ to, b^ He^ ia ^ ^fif^ ^ *
any other fort of mirror, provided they
can be traced and illmainated ^«
'(
Obferve, if* you are defirous of" pa^jtr
ing thefe forts of anadxorphofes to advan-
tage, you muft not overcharge thofe parts
tvith' colour that are mofl diftended, for
whtri 'they b^oiiie contraaecl m tte mir*
i^or ^e colours ^appefar unnatural. In a
worff,' gk^eiit attention is neceffary in draw^
ing JtnST'jpaintiiig thefe fuhjefts, as on that
the ftiocefs principally depends.
- ♦ The geometric methdd of drawing 5eformc^
^b)9<^sj^ be feen in a prifm^ will be found tt
large in the trcatife of ^h}^ NoUet.
REGRE-
- R E€ R ^ AT i a N XX^Xl
Qpf.k^ appmranceiu . » :
C\^ all our fenfes the. fight is certainly
nibj?<ft to the gre?ite^ illufion. The
various writers on optics baye defcribed a
great aiijmjter: oC.inftancea .irO. wbifl^ k de-.
cdives q^, and have qonftsuady en^ff Vf^
ed to invefUgate the caufes, to explain
their efFedsT, and to recoj^gile a.ppe;araace
with reality. We every day^ difcoyjjf new
phenomena, and doubtlefs many more are
referved for pofterity. It frequently hap-
pens, moreover, that a difcovery whtch at
firft feemed of littre confequcncei feas ted
to matters of the higheft impbrtiance.* '
Take a glafs bottle A, (PL XIL Fig. 4.}
and fill it with water to the point B; leave
the upper part B C, empty, and cork it
in the common manner. Place this bottle
oppofite a concave mirror, and beyond its
foQus, that it may appear revjcrfed, and be-
fore
12^ RATIONAL
fore the mirror (fee aphorifm 4, pagie?
65.) Place yourfelf ftill further diftant
than the bottle, and it will appear to yotf
in the fituation a^ b^ c^ (Fig, 5.)
Now it is remarkable in this apparent
bottle, that the water, which, according to
all the laws of catoptrics, and all the expe-^
riments made on other obje(3:s, fhould ap-
pear at a b^ appears on the contrary at b r,
and confequently the part ab appears
empty.
If the bottle be inverted and placed be-*
fore the mirror (as in Fig. 6.) its image
will appear in its natural, ere£l pofition j
and the water, which is in reality at B C,
will appear at a b.
If while the bottle is inverted it be un-
corked, and the water run gently out, it
will appear that while the part BC is
emptying, that oi a b'lvi the image is fill-
ing ; and what is likewife very remark*
able.
J /
; 'y A H
FtATgJET
■ ',r-- f" .:::\:]
■'\\ ■• . l,i;
RECREATJOJ^S. ii^i
able^ as foon as die bottle is enlpty the il-
Ipiioa ceafes, the image alfo appearing en-t
tirely. empty. If the bottle likewife be
quite full theiQ is no illufion.
If while the bottle is held inverted, and
partly empty, fome drops of water fall
froin the bottom. A towards B C, it feems
in the image as if there were formed at
the bottom of the part a b^ bubbles of air
that rofe from a to b ; which is the part
that feems full of water. All thele phe-
nomena conffantly appear.
The remarkable circumftances i|i this
experiment, are, firft, not only to fee an
object where it is not, but alfo where its
image is not ; and fecondly, that of two
objects which are really in the fame place,
as the furface of the bottle and the water
it contains, the one is feen at one place,
and the other at another ; aicid to fee the
bottle in the place of its image, and the
water where neither it, nor its image,
are.
Note,
laS RATid^iAL
N6ce» It lias hettot conyediived^
£Miie appetrance of reafoftr thst flbSa ^
htfioo arifes partly from dur noCBeing^ ac*
cuflomed to fee urater MpenM itta botdtt
with the neck downward, and putl]r from
the relemblance there is between the ca^
lour of the air and . that of water, which
induces us to imagine that we fee them
where they ufually are ; and this is ren<->
dered more probable by putting any co«
loured liquor into the bottle, for that wiJl
appear in its proper place (M- Cuyot.) '
RECREATION XXX.
T/^e per/peBive mirror.
pROVIDE a box ABCD (PL Xlt
Fig. I.) of about two feet long, fif-.
teen inches wide, and twelve inches high*
At the end A C place a concave mirror,
the focus of whofe parallel rays is at
eighteen inches from the reflefting furface.
At I L place a palleboard blacked, in which
a hole
^-iSpX^^'^^J^P^^ ^-^f^P'^i *V9?)?.A.tp I,
clofc, that the mirror H, nyiy be entirely
a.fi»uze; ^ ^ '
'^Ma^^n apertiire at'^^near thcrt8p df
Ifee M&^^%i^ teneatfe wtiicK, on t^c m-
■fi3e, pkee, iti!(iicceffion/palAtmgslo'f'aif-
fer^'fafcj^aS/ *8 Viftis; landfeaj)^, Sec.
fo that tiiey may be in front of the mir-
ror He Xl^t thei)6x be fa fdaced Aat tht
objeft may be ftrongly illumined by the"
fun ; or by wax lights pkcQd under the en**
dofed part of the box; A L ;.. q . y :j ■ ,; t
- ••. . > '. " ->■ ' ' -^^^ .
' . By this fimple coriftruftion the.objeSti!
~ -^ ■ • . • ^ '1 • . ■ ... -
placed at G D will be thrown into, thcit
natural perfpedive, and if tjje fabjedlti be
prdpferly chofe, the appearance will ht
altogether as pleafmg a$ in .optica^l mar
.chines of a much more complicMed form^
, Vol. li, K Nctc,
\
I30 R A no UAL
Note, A glafs mirror fhould be iiw»fsi
here ufed, as thofe of metal do not^re*
fent the objeds with equal* vivacity, and-
are befide fiibject to tamifh^ It is alfo ne;-
ceffary that the box be fufHciently large,*
that you may not be obliged to ufe a* mir-
ror whpfe focus is too fhort; for m that
cafe, the right lines near the border of the-
.pidlure will appear bent in the mirrOr,e»
which will have a difagreeable effc4J:^ an4»
oannot be avoided.
RECREATION XXXI.
^o Jet fire t(K a cbmbufiibk bodjr by ike re^
fleSHon. of two cjmcate mirrors.
np HE rays of a luminous body placec^
in the focus of a concave mirror bet-
ing reflected in parallel lipes, if a fecond
mirf or be placed diametrically oppofite the^
firft, it will, by colledting thofe rays in»
its focus, fet fire to a cpmbuftible body..
Pkce'two concave mirrors, A and B-
(PI. XIIv Egr 2.) at about twelve or fifteen
'feet
feet diftance from each other, and let the!
axis of each of them be in the fame line.
in the focus C, of one of thorn, place a
live coal, and in the focus D of the other*
fome gtlripbwdef i With a pair of double
bello^si Which inike a continual blaft,
kecjp conftantly Mowing the coal, and not^
^^ithffanding the diftance between them the
ipavrier will prefently take fire^
It is not iieceflary that thefe mirrors bei
of metal pr glafe^ thofe made of yirood or
pafteboard, gilded, will produce the explo-
fiony Which has fbmetimes taken efFedt at
the diftance of fifty feet, when mirrors of
eighteen inches or two feet diameter hav6
bcec^ufedi
This expferiment fucceeds with more
difficulty at great diftances; which may
proceed from themoifture in a larg€ qtfen-»
tity of .air. It would doubtlefs take efi^dA
more readily, if a tin tube, of ain. equal dia-
meter with the mirrors, Were to be .placed
betMreen them.
Ka RECRE-
132 R A T I 6 N A L
I ...
RECREATION X^LXIL
The real apparition^ ,,
OEHIND the partition AB (PI. .Xlt.
Fig. 3.) place, in a pofition fomc-
thing oblique, the concave mirror EF,
which mufl be at lead ten inches in diame-^
ter, and its diflanci^^rdin the partition equal
to three-fourths of the diftance of its center.
In the partition make an opening of
feven or eight inches, either fquare or cir*»
cular : it muft face the mirror ; and be of
the fame height with it. Behind this par-
tition place a ftrong light, fo difpofed that
it may not be feen at the opening, and may
illumine an objedt placed at C, without
throwing any light on the mirror.
Beneath the aperture in the partition
place the objefl: C, that you intend fhall
appear oh the outfide of the partition, in
an inverted poiition ; and which we will
fuppofc
RECREATIONS. 133
fuppofe to be a flower. Before the parti--
tioHf and beneath the aperture, place alit*
tic flower-pot D, the top of which (hould
be even with the bottom of the aperture^
that the eye, placed at G, n^ay fee the
flower in the fame pofition as if its ftalk
eame out of the pot.
Xag^ep^q to paint the fp^^^
back part of the partition and the mirror
black, to prevent any reflexions of light
from being thrown on the mirror ; in a
word, fp difpofe the whole that it may be
as little enlightened as poflible.
When a perfon is placed at the point G, he
will perceive the flower that is behind the
partition, at the top of the pot at D, but on
putting out his hand to pluck it, he will
find that be attempts to grafp a ihadow.
Obfervation.
'I ' ■ ^
The phenomena that may be produced
by means of concave mirrors are Jiighly
K 3 curious
134 R A^ I O N A ^
Cf^pus and aftoniihing. By theif ^14 fpeos
fiwPPPAi fof example, you wer€.^.tftftwy
j)fece, h^ fl»pi^ fee tfee 4pp^tip«luB^;:.»
ftbifent pr deceafed friend (of whflf« pOft-
trait you are in poffe^on). I9 order iq
produce this phantom, inftead of the hole
in the pwtttion A B, ia the laft %u*«!ithere
inuft be a door, which opens into an apart*
inent to which there w a confiderable de-*
<cent, Under that- door you ?Lre to place
the portrait, which muft be inverted an4
ftrongly illuminated, that it may be lively
reflected by the mirror, which muft be
large and well poliihed, Thea having ,
introduced the incredulous fpedator at an^
other door, and placed him in the proper
point of view, you fuddenly throw open
the door at AB, when, to his great aftor
pifhment, he will iminediately fee the apr
parition of his friend.
It will be objeded, perhaps, that this is
ffot a perfed apparitjop, becaufe it is only
6 vifible
r
1
r,
04.
Flate.xii.
V
B
/■
D
c/y\
VvFl
\J
•^
'» •
IN .
m
?./^Jtft Sjh^
■ I
flE CREATIONS. 135
pat. one point of i^iew, and by oneperfon.
£mt it ihould be ^remembered) that it wtt
^n eftabliihed maxim in the laft.centufiesi
^hat a fpedre might be jr4{ible4;o one per-
:fon and not to ptbers. JSo .Shakefpeare
'makes both Hamlet and Macbeth Xee:app»r
^itions that were nqt yifiblc to others, pre«-
ifent at the fame time* It is not unlikelyi
■moreoYeCs that this jnaxim took its rife
from certain apparitions of this kind that
were raifed by the monk$, to ferve fome
purpofes they called jeligious ; as they a-
,Ione were in pofleflion of what little Jearn^
4ng there thea was in the world*
Nothing here faid is intended to rinvali-
*date the belief that feparate fpirits may
:hold Gpnverfe with men. He muft be
■either very weak or very wicked, who can
wifh to difbelieve an opinion that is fo
ihighly honourable and^ advantageous to
.humanity.
There is one phenomenon we muft not
ih^reomitj fortho' it be common enough,
K4 it
136 RATIONAL
it is alfo pleafing, sind eafy to be perfornirf
e8. If you place yourfelf before a concave
mirror, and at a proper diftance,your figure
will appear inverted, and if you ftretchout
your hand toward the mirror, you will
perceive another hand that feems to meet
and join it, though imperceptible to the
touch. If inftead oiF your hand you make
life of a drawn fword, and prefent it in
. fuch manner that its point may be direct-
ed toward the focus of the parallel ri^y^
of the mirror, another fword will ap-
pear, and feem to encounter that in
your hand. You are to obferve, that to
make this experiment fucceed well, you
muft have a mirror pf at leaft a foot in dia-
meter, that you may fee yourfelf in part.
If you have a mirror large enough to fee
your whole perfon, the illulion will be much
more ftriking. This phenomenon, with
which fo mifch parade has been made by
fpme modern experimental philofophers,
yas defcribed by Baptifta Porta more thsii^
apoyea^sfmce.
CHRO^
RECREATIONS, 137
CHROMATICS.
/CHROMATICS 18 that part of optics
which explains the feveral properties
of jthe (so^pufs of light) and pf natural
bodies.
DEFINITIONS.
1 . Thofe rays of light that are all equally
refrangible, are called fimple or homogc-
Qial rays.
2. Thofe rays that have difFer-ent de-
grees of wftapgibility, are called com-
pound, or heterogenial \
3. The colours of homogenial light arc
called primary or fimple colour9 : and
4. Thofe of heterogeneal light, fecon**
dary of f ompound colours.
5. A fpedlrum is a coloured image of the
fun, produced by the refraction of a ray
pf light let into a dark chamber.
* The ter(n$ bpmpgeneal and heterogeneal are
derived from the Greek wf»rds otnosy the fame ; eUroSj
pother \ and genos^ kind ox fpecuu
6,A
138 RATION At
6. A prifm is a glafs body^ whofe two
«nds are ilmilar ^nd fttratIel.tri]aigI)eB,.and
^ts three iides regular planes^
*■»»■-
APHORISMS.
1. All the colours in nature proceed
from the rays of light.
2. There are feven primary colours,
^hich are red, orange^ ydlow, green^ blue^
indigo^ and violet.
3. Every ray of light may be ¶te^
into the feven primary colours.
4. The rays of light in paflj^g through
the fame mediuni tave differjeiiit d^grecf
of refrangibility.
5. The diflference in the.coloura of Ugbt
arifes from its different refrangibility, that
which is the leaft refrangible producing
Ted, and that which is the mojft r^fraiigiir
i)]e, violet *.
* It IS conje£lured that the different refrangibility
Ifl the rays of light proceeds from their differeat
♦magnitude : thofc pf red lights* being the largeft,
mak*
RgCR^EATIONS. 139
T Jin 9y ^wn^Qfta^iog ady two of the
X p€ir^i^ jpoloursy jis Fe4 Andydlow, or yelr
}pw and b}ue, th« lotermedirtte irolour^ as
pjan^e origften^ maybe produoed.
7. The colours of bodies arife from their
llifpofitioas to li^efle^ one fort of rays, and
$0 abibrb the other, Thofe that refledt the
leaft refrangible rays appearing red j and
thofe that refledt the moft refrangible,
violet*,
make the ftrongeft impreffion on the retina ; «n4
Ihc/ie of yioh^t, being the finajleft, make the weak^
left impreffioQ.
* It appears highly probable, from obfervations
made by Sir Ifaac Newton, that the difpofition of
bodies to refle£l: the difFerent rays of light, arifet
(rorh the different fize 'of their particles.. Thus,"
fhe aiure colour of the fky, and the nioft luminous
*lRhite, as that ofiilietals, he fuppo&s to he produced
)>y particles of the fir^; order ; but if the white be
)efs intenfe, as that of linen, paper, and fuch
like fubftances, he conjectures that it arifes from a
mixture of particles of all orders. The green of
vegetables he fuppofes to proceed from the third
prder, and the particles that caufe blacknefs, to be
(bailee thanthoie that produce any of the coloMrsr.
8. Such
140 RATIO N A L
8. Such txxliee as refledl two or more
forts of rayS) appear of various colours.
9* The whitenefs of bodies arifes from
their difpofition to refled all the rays of
light promifcuoufly.
lo. The blacknefs of bodies proceeds
from their incapacity to refled any of the
rays of light *,
RECREATION XXXIIL
Out of a Jingle colourlefffay of light to pro-^
due ef even other rays^ which Jhall painty
on a white hody^ the feven primary co-*
lours ofnafurq.
pROCURE of an optician a large glafs
^ prifm P E F, (Plate XUL Fig. i .) well
polifhed, two of whofe fides muft coa-i
tain an angle of about fixty*four degrees.
Make a room quite dark, ajid in the win-
dow Ihutter A B, cut a round hole, about
* From hence it arifes that black bodies, whfo
cxpofed to the fun, become fooner heated than all
others.
one-
RECREATIONS. 141
one-third of an inch in diameter at Cv
* I
through which a ray of light L I paflingy
falls on the prifm DEF, by that it is
refrafted out of the direftion IF, in which
it would have proceeded into another G
H, and falling on the paper MNSC,
will there form an oblong fpedrum P Q^
whofe ends will be femicircular, and its (ides
ftrait; and if the diftance of the prifin fron^
the paper be about eighteen feet, it will
be ten inches long, and two inches wide.
Now this fpedrum will exhibit all the
- primary colours ; for the rays between P
and V, which are the moft refracted, will
paint a deep violet ; thofe between V ?nd
J, indigo ; thofe between I and B, blue ;
thofe between B and G, green; thofe be-
tween G and Y, yellow ; thofe between
y and O, orange; and thofe between O
ajid R, being the leaft refraded, a^ in-
tenfe red*. The colours between thefe
* For thU reafon it is that the rays which are
near the edges of a lens have diiFerent degree? of
refradlion,
i42 ft A T ro N A t
ipaces will not be'eYcfy yrtiere equally itt«
tenfe^ but will incKne toUbje neighborui^
ing colour} tlms tke pdrt of the ofahgd
liext to Kj 'bv^ill indiiie to a redt and that
next to Y, to a yellow; and fo of tbef
reft.
REC.RfiATlON XXXlV.
From two or niof-d df ifie prirhar^ colouf'Si
to compofe others that JhdlU in appearance^
refimble'thdfdoffhef9tmn
13 Y mixing the two homogeneal cofbur*
red and yelIoN?v, an orange wfll btf
produced^ fimilar in appearance to that
in the fericsr of primary c6lolirs} but the
light ofj^e one being honiogeneal, and
that of the other heterbgdheal, if the for-
mer be vievired through a prifin it will re^
main unaltered,^ but the othei* will be re-
folved into its component colours, red and
yellow. In like manner other contiguousr
rcfra<aion, and tinge the oh]t8t with difFe'rcnt co-
4ours.
ho-
RECREATIONTS. 14J
Ikomogemal colours may compound new
coldiirf J aB by mixing yell6w and green, »
colour between them ia fbrroed; and if blue*
be added, there will appear a greetithat is-
the middle colour 'of thofe threei* For the*
yellow and Wue, if they are* equal in quan*
tity, will* draw the intermediate green
equally toward .them, and keep it< as it
were, in equilibrio, that it verge not more-
to the one than to the other. To this-
compound green there may be added fome
red and violet, and yet the green will not
immediately ceafcj but grow lefs vivid;:
till by adding more red and violet it will
become more diluted, and at laft, by the
prevalence of the added colours, it will
be overcome, and turned into whitenefj^
or fome other colour-
In like manner if the fun's white, com>-
pofed' of all kind of rays, be added to any
feomogeneal colour, ; that colour will not:
vanifli, nor change its fpecies, but be di-
Uited;^! and by adding more whitej. it wilt
become
144 RATIONAL
become continually more diluted. Laflf^^^
if red' and violet be mixed, dierewill be
generated, according to their various pro-
portions, various purples, fuch as are not
iike, in appearance, to the colour of any
homogeneal light : and of thefe purples^
mixed with blue and yellow, other new
colours may be compofed.
RECREATION XXXV;
Out of three of the primary colours^ red^
yellow i and blue f to produce all the other
prifmatic colours y and all that are inter^
mediate to them.
pROVlDE three panes of glafs of About
five inches fquare, (fee Plate XIII.
Fig. 2.) and divide each of theifi, by pai-
rallel lines, into five equal parts.
Take three flieets of very thin paper,
which you muft paint, lightly, one blue,
another yellow, and the third red *• Then
♦ You muft ufc water colours for this purpofe :
the blue may be that of Pruilia, and very bright;
the
RECREATIONS. 145
l^fte on one of the glafles five pieces of
the red paper; one of which muft cover
the whole glafs, the fecond only the
Four lower divifions, the third the three
lower, the fourth the two loweft, and the
fifth the laft divifion only. On the other
two glafles five pieces of the blue and yel-
low papers muft be pafted in like man-
ner. ,
You muft alfo have a box of about fix
inches long, and the fame depth and
width as the glalTes : it muft be black on
the infide: let one end be quite open,
And irit the oppdfite end there muft be a
hole large enough to fee the glafles com-
pletely. It muft alfo open at the top, that
the glafl"e8 may be placed in it conve-
niently.
When you have put any one of thefe
glafles in the box, and the open end is
the red, carmine; and the yellow gambooge, mix-
ed with a little fafFfon. Thefe colours muft bq
laid very light and cven^ on both fides of the
paper.
• Vol. ir. L turned
>46 R^,A'.TjPDN.;AX^ >,
turned toward the^fun* you^l^.ife^.^ee^
difliad); ibades .of the colour it^^^taii^. . .
If you pkc« the blue aiid yellow giafles^
togethoTi in a fifnilar. dire^gpi >ypu twillr
fee five fliades of green diftindlly formed*.
.When the blue arid red glafles afe|>lhd^,.
a bright violet will be produted^, aftd by
the red'^d: ytilbw^ the icttrad fiiad^s of
©range. '^ ■ \ '^
■^milar politldn, yoii place tHeliiicAB
#f the yellow clalsi agalnft^tlje Me ^t>
.©f the Wiie, (Ate S^H. Fig:' j^-j^you wjU
f(Je all the various greens tjiat 'pflToduc^^^ by
ntiture * ; if* ^ jne' plue and. r-ita' glaJKs , h
plaoed 1^ that mannerr you wu£,have all
l(?te poflible Varieties or purples, violets^
Stc and laitryi ii the red ?ind orange
^ . :^ teth^ffft^H^ilDn -of tile jMB^'^^ <^^
ef green was conftamly vtfible : but by thus in*-
,;:afi/^yigi.til?ngl#«i.!^^SHW^^ i)fthc<S9^P«« be-
ing conftantly uneqoial^ » very {^e^fi^g )H^^]^^^^
, tiirts IT prcJuccd. - i
^'l^mht^'^fS^kc^^^^^^^ ^^lI^be ^11 the
awora, &c.
R'BG^rfe A'T*'10N XXXV!.
. '' y^ilowyj%is^lu€i^^ Jpgtthermth light and
\. Jfya4ii^ iM.^^^m^^llr:thf^ gradations (^
the prijmattc colours^
, ^ papefcs tliat are painted with thefeven
Fnfmatic colours, in the fame manner as
. ;n the laft Recrea^pn. The colours for
the orange, er^en, indigo, and violet,
*/''] ;;'jv.;'b(;Tq Ji»?, • -m '.':'. i.-, b«'ft;'?.v -j; 1 ; y .. ;^
ipayjbe made by missing the other three*
Then voth biftre *, well diluted, fliade a
flieet of v<;ry thin paj^erj by laying it light
qn botl> its (idcs. With pieces of this pa«
{>er cover four-fifths di a glafs, of the Ijunc
iaSi> wkbcfaii^ ochecs^'lv^ laying one piece
oh the four kiweft^^ivifions, another oa
' •^^T^ ^Bl^ t»fe tlfeJlnttft be made of foott
L? the
J48 RATIONAL
the three loweft, a third on the two low^
eft, and the fourth on the loweft divifiort
only : and leaving the top divifion quite?
uncovered^
When one of the coloured glaffes i^
placed m the box, together with the glafs'
of fhades, fo that the fide AB of the
one be applied tathe fide BC of the Other,
as in Fig. 3. of the kft Recreation, the fe-
yeral gradations of colours will appeal
fliaded in the feme manner as a drapery
judkioufly painted with that colour.
It i^ on this principle that certain French
artifts have proceeded in their endeavour*
to imitate, by defigns printed in colours,
paintings in oil*: which they do by four
plates of the fame fize, on each of which.
i% engraved the fame defigiK One of
Aefe contains all the fhades tiwit are to^lke
jcprcfented, and which are painted either
black, or with a, dark grey. One of the
&ree other plates is^ coloured with, blue,^
another
RECREATIONS. 149
attotlijer with red, and the third with yel-
low: each of them being fengraved in
thofe parts only which are to reprefent
that colour *, and the engraving is either
J^ronger or weaker, in proportion to the
tone of coloiu: that is to be reprefented f. .
TJtiefe four plates are then paffed ^Iter-
fiately under the prefs, ^and the mixture
of their -colours produces a print that bears
* When a red drapery is required, it is engrav-
ed <in^the plate affigned to that xrolour ; and fo of
yellow and blue : but if one of the other colours
be wanting, fuppofe violet, it muft be engraved
on thofe that print the red and bWe : and fo of the;
reft. The plates of this kind have been hithert^l
engraved in the manner of mczzotinto, but thefc,i-v'.
junlcfs they ar^ ikilfiilly managed, foon bccompp^^
Anutt/. Engravings in the inanner of the crayon,
would perhaps an fwer better.
t The principal difficulty in this fort of engriv-
iiig arifes'froni want of a (kilful management, ia
grving each plitc thit precife degree of engraving
which will produce the tone of colour required. If
a bright green is to be reprefented, there fliould be
.an cq-ual quantity ef graving .on the red and yellow
plates: but if an olive green, the yellow, pla^
^uM be engraved much deeper than the red.
L 3 no
J50 R A T lOM AI-H Jl
no fmall refemblance t^ai^ioAk^g^^ H-
muft be; confciTed, however, ti^wk^t haft
been hi^^rto done of thUkiadfCif^lSiliMr^
ihoct of that degree of perfedioo^ipf ]vyhicb7
this art f appears fufceptibk. If theywlp:
engrave tJxiB, hefl: . ipi the manner of the^
crayon^ /were to apply themfelves to this
iart, there is reafon to expe£t they would
produce far more finifhcd piece* than w^
have hitherto feen.
- li
f R E C R E A T I O N XXXVll; '
The magical prifm.
li^AKB a hole in the window-fhutter of
a' dark room, through which a broad
beam of light may pafs, that Is to be re-
fjrafted by the large glafs prifm ABC,
^late XIII. Fig. 4.) which may be made
df piedes of mirrors cemented together,
and filled with water.
Primde ancfther prifin DE'F,' Wade of
thiee pieces of #6btlj idiroiij^Hiie intddle
: : of
rrWto tevdl^. This priori' 'rtitilPBt i(i8i?'
Ti»fcd wth VMte ^per/ and leadt' of itaf /
' fi&s^ «it ttedtigh In ifevet^l 1^^^
rtj^Wftflt^ different iigiiftfsi 'aiid»tli6fe oF ^
«4ihfide^iteMM likewife tfe different/The
Ihfide of this' prifm rS tb beiibllow,"' aiid'
made quite 1>lack, that'itiilay Vi6t Wflcfft
atny of the light fhat paiffes through ffid
fides into it.
When Ais prifm is placed near to that
of glafs, as in the figure, with one of its
fides EF, perpendicular to the ray of
ligiit^ tjie figures on that fide w^l^ Fl^!^
perfedliy white: b.Ht when it jcomes^intb
the pof^tioijL ^ >^, the figures wilji, ajypcajr
yeUckw ai^d.Ked^ and when iti^Jfi th? pp^
fition kjy ,t^ey wiU appear, Wueja^d violet.
/Skj5 the pi;ifmas turned ro^indits aj^i^,* the
other fides will have ^ figi^lar ,appearai[ipe*
If inftead of a prifm a four or five-fided
, figure be ^(Ejrp* ufed,...tU^r ^ppearjinceiSJwiU
X4 Thi«
X52 RATI O N A L *
This phenomenon arifcsfroip^ttic differ-
rent refrangibility of the rays of Ught*
For when the fide E F is in the pofitioi^
g /li it is more flrongly Hluminated hy the
Jeaft refrangible rays, and wheretrer they
are predominant, the object will appeaB
red or yellow. But when it is on the po-
fi tion i/y the more refrangible rays being
then predominant, it will appear linge^
with blue and violet,
RECREATION XXXVIH.
. T^hejolar magic lant^n.
pROCURE a box, of about a foot high^
and eighteen inches wide, or fuch
other fimilar dimenfions as you fhall think
fit ; and about three inches deep. Two of
the oppofite fides of this box muft be quite
op6n, and in each of the other fides let
thdre be a groove, ^ide enough to pafs a
ftiff paper or pafteboard. This muft box be
faftened againft a window on which the
fun's rays fiill dir«^. The reft of &«• witt-
. , dow
4ow -^ouW |>e clofcd up,. tbaC npf Ij^ljt^
piay enter^ * .
Provide feveral flieets of fliff paper*
<whicfa muft ]k blacked on one fide. O4
thefe paperjs cut out fuch figures as yoi|
fhall think proper, and placing them al?«
jternately in the grooves of the box, witli
their blacked iides towards you, look at
•fhen> through a large and clear glafs prifmj
and if the light be ftrong, they will ap-
pear to be painted with the moft lively
colours in nature. If you cut on x)ne of
thefe papers^ the form of the rainbow,
about three quarters of an inch wide, yon
Will have a lively reprefentation of that in
the atmofphere.
Thi3 Recreation may be further diver-
fified^ by pailing very thin papers, lightly
painted with different colours, over fome of
the parts that are cut Outi which will ap-
pear to change their colours, when view*-
ed through ^the prifai, and to iknd out
from
from.thepapcF, :at different difliances, aw
cording tb the different degrecsiof rfsftxn^
gibilityiijof. the colours with which they,
are>^ntedi
' For 'gfcrter cottTteniencei dioprifm «ftfty
bfe'^pSiftced'^hi^ ft fltafnd on^a table, at tJftj.
height ^of-ydur leyij^ and » made ta turtt
it)uhd^ on an ^ axis^ tha* when j^u h%VfS
got an' ^VL^t^c^6^'^tofpe&y y^^
k ih' that'^poikidn. TMs 'e^perimetit
may he 'made 'at a trifling expchdej Jftid^
if properly conduiS^d, will afford no final!
entertainment. ^'^ /:•.: >^ ;i' '^ v^^.;-
, ,TAe ar/i^dal ralniow^ ■, , • .
y^FPOSlTE a window into which the
'^ fun fliines diredt, fufpend a' glaft
globe filled \^th water, Ir^ a^ilHngthit
runs ov^t a pulley, fo that the furies rays
ffiay fall oh it. Then drawing the globe
gradually
I
R EtORE A T rO N S: 155^
gradually }lpi when it comes to the height"
of about forty degrees % you will fee, by ^
placing yourfeif in a propch fituatioi, a:
purple colour in the glafs, and by drawt*
ing it gradually up higher, the other prit-
mja*ic fiolppreir blue, green, yellow, sfad
fed, will fucceffively appear; after whicb'
1^ colours wHl difappear, till the globe iflf
laaCed to about fifty degrees, when they
will again be feen, but in an inverted or-
der> the red appearing firft, and the blue
or violet laft : and when the globe comes
up to little more than fifty-four degrees
they will totally vanifli.
Thefe appearances ferve to explain the
phenomena of natural rainbows, of which
there are frequently two; the one being,
about eight degrees above the other, and
the order of their colours is inverted, as
* That IS, if you fuppofc an arch of a circle to
he drawn from the horizon to the zenith, and di-
v.i4cd into fiinctjr equal parts or degrees, the globe
muft be jraifed to the height of forty of thofe de-
grees^ ' •
in
156 RATIONAL
5n this experiment, red being tfee upper*
rnoft colour ia the Jower bow^ and violet
in the other.
The rainbow is not in the clouds, but
in the falling rain, and always oppofitc
the fun. The different order of the co*
Jours in the bows ^rifes from their diffe-
rent reflexions j thbfc of the under bow
being caufed by two refradions and one
refledion, and thofe of the upper, by tT¥o
refradions and two refledions, and there^
fore the colours of this are lefs bright thaji
"the other, their ftrength being diminifhe4
by every refledion.
Now, it ha3 been proved by repeated
cxperiipents, that forty degrees forms the
greateft angle by which the mofl refran-
gible rays can, after one re|ledion, be r^r
fraded to the eye j and that fomething
more than forty-two degr^ees forms the
gfeatefk angle, ynder which the leaft re-
frangible rays can come tp the eye after
2 . ope
R.ECREAriONS: 1^7
one reflecSJion. Therefore all the colours
of the lower bow mult lie in the fpace of
lefs than two degrees-. In like mai;iner it
has been proved, that fifty degrees make
the leaft angle under which the Icift re-
frangible rays can be vifible to the eye
?fter two refledions; and that about fifty-*
four degrees will be the leaft angle under
which the moft refrangible rays can come
(o the eye after two refledions. Thero^
fore all the colours of the upper bow muii
be in lefs than four degrees.
T
It follows from what is here faid, that
^11 rainbows are of a circular form and
equal magnitude^ and as they are always
oppofite the fun, the parts we fee of them
muft be in proportion to his height above
the horizon : when his altitude h forty
degrees, only the upper rainbow can be
vifible, and when it is fifty^four de-
grees there can be no rainbow; but as the
fun's height, during the winter half year, is
never equal to forty degrees, there may
then be always two bows vifible.
R E C R E-
^ijl R A TIOWAiB V
RECREATION* XL.
itie prifmatic tamera obfcura.
Tyr AKE two holes F»/, (Plate XBi.
"^ Fig, 5.) in the (huttcr of a dark chaise
bcfr^near to each otbcTv and againft each
hole place a prifm A6C5 and /7^r» in a
perpendicular dirediion, that their fpec-
trumd'NM maybe caft dii the pajper !n a
horizontal liiie; arid coincidid wi^ each
other; the ihed and violet of the one b*-
ing in the lame part with thofe of the o^
then Thepkpef fhbuldWpkced'kt fach
a diftance from the prifmsi th^t the {pcc-^
trum may be fufficiently dilated.
Provide fe\''eral papers nearly of the
^me dimenfion with the fpe£lrum) crofo
^thefe papers, ariddraw'lines parallel to the
di vifions of the colours. '^ In thcfe di vi fion6
tut out fuch figures as yo\i Ihall find will
have an agreeable efFed, as flowers, tree^^
ariimils^ '&c;
When
RE G R' E A rr O.M^S. ^
When you have placed one of thefe
papcrsUn its prc^riprffiaoj^ haiig^lt black
eloth or pape? behind it, that noae of the
rays that pafe through may^ bfe refle6kedj|.
4ftE*conf\[i£etbe^enoaffeQt0i!i> T]^j€gnra»
<:»H^Qn thetpftperiwilt*hj^ i^pp^arifeongiy
IlIi^miQatiied yviih al} ( th^i .ef ig}afll)fiOl(Htf^^
■r If jif^KJe/W^vof fhe;(Pi^g|8ri?eiHarp^^^ ^
jf<^, tiher'Ot]lijer. , be revolved jipait^^Mtisy
the continually alteration of the colours
wiH afford i a plealing variety j v^hichj may
,bc further increafed by turning tfic prifoa,
Ground in different diredions.
• ' • « • • j» -.
When the prifms are lb placed that the
two fpedrums became coincident in an in-
verted order of their colours, th^ red, ewd
of one falling on th^ violet, ead ^f ,the o-
thcr, if they be then viewei- through a
third prifm D H, held parallel to their
length,' th^y^wiU no Joogw^ppe^r cfanr
cident, but in the form, of/two 4iftin<|t
. . . ^^" fpedrums^
i^ kATlONAt
^ledrums, ptj and nnii (Fig* '6.) croffihgf
one another in the middley like the letteif
X* The red of one fpedlrum and Ae Vio-
let of the other, which were coiiictdent at
N M, being parted from each other hf
A greater refraction of the violet to ^ and
Mi than that of the red to^ and /^
This Recreation may be further diver-
fified byaddiiig t«to other priioiai that flxall
form a fpodrukAJtii i^he famf lie^M^
tiguous to the other j by winch not only
the variety of figures, but the viciiEtudrf
of colours will be confiderably augmentedi
RECREATION XLI.
^he diatonic fcdle of colours.
'TPHE illuftrious Newton, in the courife
of his fagacious inireftigations of thcr
properties of light, difcovered that thdf
length of the fpaces which the feven pri-f
mary colours poflefs in the fpqdrunait
exactly correfponds to thofe of chord*
that
FLATEJfm
J^Zf^jJ^
/ .'
kECUEATIONS. i6t
ihat found the feven notes in the diatonic
icale of mufic. As is evident by the fol-
lowing experiment.
On a paper in a dark chamber let a ray
of light be largely refraded into the
fpedrum A F T M G P, (Plate XIV. Fig.
i.) and mark the precife boundaries of
the feveral colours, as a^ b^ r, &c. Draw
lines from thofe points perpendicular to
the oppofite fide, and you will find that
the {paces M r/F, by which the red is
bounded j qpe d^ by which the orange is
bounded j poc d^ by which the yellow is
bounded, &c will be in exadl propor-
tion to the divifions of a mufical chord
for the notes of an odave, that is, as the
intervals of thefe numbers i, f, 4> |> 4>
Vol. 11. M RECRE^
i62 R A -r I O N Ali
RECREATION XLIL
Colorific mufic.
PATHER Caftel, a Frenchman, in a
curious book he has publifhed or»
Chromatics, fuppofes the iiote ut toanfwer
to blue in the prifmatic colours, the note
re to yellow, and mi to red. The other
tones he refers to the intermediate colours^
from whence he conftruds the following
gamut of colorific mufic
Ut ,
Blue
Ut fharp
Re
Re fharp
Mi
Sea-greeni '
Bright green
Olive green
Yellow
Fa
Aurora
Fa, fharp
Sol
. Orange
Red
Sol fharp
La
Crimfofi ''
Violet
La fharp
Si
Ut .
Blue violec
Sky blue
Blue -
This gamut, according to his plane, Is tc^
be Continued in the feme manner for the
foU
RECREATLONS. 163
following odave ; except that the colours
«> 1*^ ^^v 1-%^ «irk /^«»i:k •wr*%T%r\
are to be more vivid.
He fuppofes that thefe colours, by ftrik-
ing the eye in the fame fucceffion as tl^e
founds, to which he makes them analo-
gous, do the ear, and in the fame order of
time, they will produce a correfpondent
fenfation of pleafure in the mind. It is
on thefe general principles, which F.
Caftel has ingenioufly dilucidated in his
treatife, that he has endeavoured, though
with little fuccefs, to eftablifh his ocular
harpfichord*
The conftruflion of this inftrument^
as here explained, will fhow that the ef-
fects produced by colours by no means
anfwer thofe of founds, and that the prin-
ciple relation there is between them, con-
fifts in the duration of the time that they
refpedively affedl the fenfes.
Between two circles of pafteboard, of
ten inches diameter, AB and CD (Plate
M 2 XIV.
j64 rational
XIV. Fig. 2.) enclofe a hollow pafteboarcf
cylinder E, eighteen inches long., Divide
this cylinder into fpaces half an inch wide,,
by a fpiral line that runs round it from top
tb bottom, and divide its furface into fix
equal parts by parallel lines drawn be^
tween its two extreraities ; a& is exprefleA
in the figure.
Let the circle A B, at top, be open, and^
let that at bottom, CD, be clofed, and fup-
ported by an axis or fcrew, of half an inch-
diameter, which muft turn freely in a nut
placed at the bottom of a^ box we fhalL
prefently defcribe. To the axis juft men-
tioned adjuft a wooden wheel G, of two
inches and a half in diameter, and that ha^
twelve or fifteen teeth, which take the
cndlefs fcrew H. Let this cyliader be
inclofed in a box I L M N (Fig. 3.) whofe
bafe is fquare, and at whofe bottont-
there is a nut, in which the axis F turns.
Obferve, that the endlefs fcrew H, fliould
come out of the box, that it may receive.
RECREATIONS. 165
the handle O, by which the cylinder is to
be turned.
This bax being clofed all round, place
over it a tin covering A, which muft be
perforated in different parts ; from thi«
cover there muft hang three or four lights,
fo placed that they may ftrongly illumine
the infide of the .cylinder. In one fidp of
this box (which :fhou3d be covered with
pafteboard) cut eight apertures,, ^, ^, r, ^,
^,yj ^, ^, of half an inch wide, and one-
third of aii inch high ; they muft be di-*
xedly over each other, and the -diftance
bet^yeen them muft be exadly two inches.
It is by thefe openings, which here corre-
fpond to the mufical notes, that the various
jcolours analogous to them, are to appear ;
and which being placed on the pafteboard
cylinder, as. we have fhown, are reflected
by means of the lights placed within it.
It is eafy to conceive, that when tfie
hjinidle O is turned, the cylinder in con-
^ ^ feq^uence
i66 RATIONAL
fequence rifing half an inch, if it be turned
five times round, it will fucceflively fhow,
at the openings made in the fide of the box,
all thofe that are in the cylinder itfelf, and
which are ranged according to the direc^
tion of the inclined lines drawn on it. It
is therefore according to the duration of
the notes which are to be exprefled, that
the apertures on the cylinder are to be
cut. , Obferve, that the fpace between two
of the parallel Jines drawn vertically on
the cylinder, is equal to one meafure of
time, therefore for every turn of the cylin-
der, there are fix meafures, and thirty
meafures for the air that is to be played by
this inftrument.
The feveral apertures being' made in the
fide of the cylinder, in conformity to the
notes of the tune that is to be exprefled,
they are to be covered with double pieces
of very thin paper, painted on both fidea
with th€ colours that are to reprefent the
- inufical notes. ^.
r J' u
^A, .
fi/W-
^
llfitft-Oftn J'hATEJnv
Fiff J^p, mt,
^ h c df
e, f ^
'~T^
\m \n
\
I 'I
t~~fe # W~^6
It
-JM-
^
V .',
RECREATIONS. 167
This Recreation might be executed in
a different manner, and with a much
greater extent ; but as the entertainment
would not equal the trouble and ex^-
f ence, we have thought it fufEcient to give
the above jpiece, by which the reader will
bie enabled to judge how far the analogy
fuppofed by F. Caftel really exifts.
This article is taken from M. Guyot,
who, though he commends the good fa-
therms ingenuity and induftry, attributes
but little merit to his fchejne. Not hay^
ing feen F. CaftePs book, we cannot pre-
tend to judge of the nxerit of his plan. It
is evident, however, from the foregoing
Recreation, that there is a much ftronger
relation between founds and colours thaiji
M* Guyot feems to imagine.
1^4 PER-
i6S RATIO HAL
ftks?E<:rivi: recreations.
If the following recreations do ndt d^
redly belong to optics, they have fp
great a refetnblance to it, that perhaps
they could not be introduced any wher^
elfe with fo much propriety^
ANAMORPHOSES,
RECREATION XLIIJ.
To 3raw on a plane furf ace an Irregular J}r
gure^ wliichf ' when Jeen froip a proper,
point of view, will appear exaBly Jimilar^
to a given figure^
•
^^N a paper or paftcbo^rd draw tl?e pa|*
*^ rallelogram ABC D (PL X¥. Fig.. i^
of what fize you pleafe, provided the fides
A B and C D be longer thaq. A C an4
B D ; let it be, for example, four inches
long and three wide. Divide it into twelve
pqual parts, and each pf thofe into foui:
Other
RECREATIONS, 169
/other equal part? *• On this paralldograji^
^raw the> regular figure that you wqi4.4
have reprefented^ in a diftorted form, oi)
jthe plsine.
Draw- on a paper the liae B]A (Fig. 2.)
indefinite toward A. Diredly over the
point B, mark the point of view. C, and
let fall the perpendicular C B. On the
line A B mark the point D, and draw from
the point of view C, to that point D, the
line C D* On the fame line, and at a con-
yenient diftancie from the point C, draw
fhe ^ne F G, of the fam^ length with AC
(Fig. I .) let it be pCTpcndjcular tp thf Iwc
C D, and by which it muft be bifeded.
From the point C to F and G, draw the
%wo lines CF and C G, and continue the^ f
^U they meet tlie Une A Bat the points
UandO, ^
♦ The fmaller the divifions arc, -the more cafy *
it will be to reprcfcnt the fubjeil wkk PfC*. *
cifion.
The
170 RATIONAL
The line H O will then appear to the
eye at C of the fame dimenfion with the
lineFG, which is equal to the width of the
parallelogram A B C D, as muft neceflairily
follow from the principle laid down in
tlie part of Optics ; that is, becaufe both
thefe lines appear under the fame angle
HCO.
Then divide the line F G into the fame
number of parts with the fide of the pa^
rallelogram A C, (Fig. i.) and from the
point of view C, to the line A B, draw the
fines C I, CL, C M, C N, through the di^
"vifions ia the line F^G.
On another paper draw the line AB
(Fig. 3.) equal to the line C A, (Fig. 2.)
and ^t k-s extremity B, eredi the indefinite
perpendicular B C. From the point B of
the line A B to the point E, in the fame
"fine, fet off a fpace equal to the line C F.
(Fig. 2.) At the point E divide the line
A B by the perpendicular H I, equal to
RECREATIONS. 171
CD, (Fig. 1.) that Is, equal to the length
of the parallelogram. This line muff:
alfo be divided into two equal part? by the
line A B.
From the point B to the points H and I,
draw the lines B H and B I, and con-
tinue them towards C and D. Take
the diftances that are between H and
I^ L D, M and N, (Fig. 2.) and tranf-
ppfe them to the line AB (Fig. 3.) from
A to I, L, M, N, O, and draw the lines
* Y, Z, perpendicular to each of thefe divi-
fions. Divide the line C D Into eight e-
qual parts, and draw the lines B G, B Q*^
BR, BS,BT, andBV,
Thefe divi fions being made, the trape-i-s
;zium CHDI will be divided into as many-
parts as the parallelogram ABCD, (Fig. i ,)
and all thefe divifions, though of them-
felves irregular, will appear to the. eye,
5vhen placed at the point C, (Fig, 2.) of the
fame
J72 RATIONAL
figure and magnitude as the parallelo'*
gram : all the lines that form the divifions
included in the trapezium CHDI, being
feen under fimilar angles. In order to
facilitate the tranfpofing the feveral parts
of the 4efign contained in the parallelo-
gram, to the trapezium, it will be proper
to number the principal divifions. The
.whole, moreover, Chould be traced with
great precifioij *. pbferve, that all the
right lines in the parallelogram form aj?
many right lines in tjij^ trapezium, there-
fore when you have piarlced their extremi-
ties, you may draw thenj with a ruler ^
from one point to the other. With re-
gard to curve lines, you will judge of their
diredion by the points where they cut the.
^ivifions of the paralklograma, aiid tf apfV
* This method of drawing an irregular figure 19
taken from M. Guyot, and differs from thofe th^t
are given by Niceron and Ozanaoi, as ki ^pp^^s
more exa£l to pla<:e the defign that is to oe lepre-
fcnted in fuch manner that the ray, or principal
point of view, may fall perpendicular on the center
of the fuppofed pidure placed at F G.
pofe
7
• * V
V&lMj^ i73
\
RECREATIONS. 173
pofe them to the corrcfponding divifions
of the trapezium.
Note, care muft b^ taken that the pa=*
per on which the diftorted figure is drawn
be well ftretched on a plan6, that its fur-
face may be quite even. You £bouId alfa
examine it attentively from the point of
view; and for that purpofe it will be con-
venient to have a little circle of brafs,
through which a hole of about two tenths
of aa inch is made, and placed upon a ftand
(fee Fig. 4.} By that overture this piece of
perfpedive illuiion will produce an agtecr
able furprize.
Obferve, that the diftance of the point
of view from the pidure may be taken at
pleafure> prodded it be not lefs than iti
width. Whett the point of view is near
the pidure it appears more deformed than
when it is at a greater diftance, for the
parts then become more extended toward
CD : from whence it follows, that if we
would
174 RATIONAL
would execute a defign of this, fort on th€f
fide of a gallery, it muft be regulated ac-
cording to the dimendons of the part on
which it is to be drawn. Thefe fub-
je6:s, when well executed, at full lengthy
are highly agreeable, and appear the more
extraordinary, as the eye not being able to *
view them but by parts, (when walking in
the gallery *) we cannot form the leaft idea
of what they will prefent when feen from
a proper point of view, where the efFed is
' truly admirable.
♦ There are, at the convent of Minims in tSe
Place Royale at Paris, feveral fubjef^s of this kind,
painted on the walls of the cloifter by P. Niccron,
who has publifhed an excellent treatife on this art.
Among others, the figure of a Magdalen daily ex-
cites the curioiity of a number of cdnnoiiTeurs.
Unfortunately, thefe pieces, which have fufFercd hf
time, have not been properly repaired.
RECRE-
REC:R RATIONS. 175
R E C R E A T I O N XLI V. ,
Tq draw an Irregular figure on a plants
which being feen from two oppofite points
of viewp Jhali reprefeni two different
regular objeSIs^
TV/FAKE choice of a plane of a convctaf-
ent fize, fuppofe two feet long and
half a foot' wide. Draw the line A B of
the fame length, (Plate XVI. Fig.i.) conti-
nue it on each fide to C and D, and ereO: the
perpendiculars CF and DG to the he^ht
of about three inches. Draw the tines
A F and B G, and divide the line A B into
fix equal parts at the points S, (or into any
otherjnumber you fhall think fit). From the
two points of view F and G draw the lines
F S and G S, to thofe fix divifions.
Then on the line G AfetoflFthe diftance
GB, and on the line FB the diftance FA^
and draw the two lines B H and A I, which
will determine the width of the two fub-
jeds
jeOtsyof :«re!to rreprefeat.iottfAher pland,.
and are fxt iteyiime^ th^lddeTdDai the
point F, and .the pther fromr^G;. iad of
which the unequal dtyinoas forntfedby the
lines GS and FS, will deterhfinethore that
are to correfpond to the feparate and hi4
clined parts of the irregular figure which
is to be feen from the points of view
FandG. ■ • - ■'•^
This fifft-prftparatioii being Yiikd^ draw
the parallelogram ABCD (Jig; i.) of the
fame length with the line AB iflt the
■ , ..\ . '• - ■ ' n* ^ .' • - v.: ..J- ,.,. .^^- ..
prcecding figur^i ^^ ^^V^? fis ilfictf «
wide; divide^ it into two e^uaKjparj^ hj
' the line E G,^ which continue to H^ac^d, ly
(qual to the Alliance there is betysreenCA
andBB(Fig.i.)^ ::::.■
From the points AaSB-{^ig.. j .} kt fall
the perpeiidiculars A A, , Q L, S L, and P C*
on the line AC (Fig. 2.) and from, the
points L dras? the linesf li,M ff^.^Hv^
*AB. ■' ■■ '^"" -"-'■•■ „;1:^' ■ '" .;
T- Erom
RECREATIONS. .177
From the four angles of t&e panlldo->
gram ABCD>,draw the lines Aland BI
to the pomt of view I, and thofe of C H
and D H to the other , point of view H ;
thefe lines will determine by the feflions
at X and Y the apparent height of the
figure*
Then divide the lines A B and CI), in-
to as many equal parts as you fhall think
proper, and from thofe points draw the lines
NlandNH.
Next, draw on a paper the two paral-
lelograms F G H I, L M N O, (Fig. 3.) arid
on them you are to draw the two different
defigns that you would repirefent in the
diftorted figure. Let each of thefe paral-
lelograms be of an equal height with the
diftance XY, (Fig. 2.) and of the fame
length as li B (Fig. 1.) Divide their
height F H or LN, according fo the divi-
fions of the lihe X Y (Fig. 2,) and their
length H I of N O^ accof.ding to thofe of
ihelineBH(Fig. k)
' Vol. II. K After
fyS R AT I O N ALr
• After having Hrawn the two defigpotv ^^
corre&ly as poffiblc, on the divifiona jiift
meotioned^ take a board or pafteboardB
AB G D- (Fig. 4.) of the fame dimenfion^
with the paralklogram AB G D^ (Fig. 2.)
and oa it draw the lines L M^ com^pcmd^
ing to the perpendiculars let fall frobi O;
(Fig. I ) Thefe lines fhould be drawn fuf«
fieiently deep to admit the £bMa of paper*
hex^eafter mentioned*
Take ai very thin paper AB€JD (Fig. 5.)?
of about two feet and a half long, and (ix^
inches wide, and on it draw p^aUdtUnesj,^
at diftances correi]3onding to A O^ O S|,
S O, &c. (Fig. I .). which you will meaiiicq^
with acompafs from the aijgleaon the fiuM^
AB(Fig. I.) . ,
Divide this paper into two equal pjRrtf'
by a line drawn from the points X and Yt
and obferve that it is on the fpaces A^ b^ b^
&c. that you are to draw the irregular fi«^
gure which is to be feen from the point F^
6 ,and
a A t^ O ! 1 A Jl
V\ f-
ri jcna^bb
^l^rl TuaEjm. \
H^l ^nodiv^ib Qih no ^'yl.i'iirr
tnDrlixdmiii ^rr
MM M M M W%
:.i^: r.^: :;^' ••-;.'
j^ ;rv:
kEGREAfiO^S; i^0
iad oii thofe of ci r, c; &c. that irliidk il
to h6 feen from the point G;
dri e4cix of thcfe fpaces df 2(w the fiftesi
iiot pundiiatted, of the pafallelog^tti
ABCD (Fig, 2.) that terminate iii th^
points ri and I; Then trace on the faffitf
|kper an the ftfo)te« ri^the two figures
drawn on the two pamleldgfams, (Fig. 3.)
tarefelly obfervmg the feveral divifions iaf
i^hich they correfj^rid.
Wheil this irregulaf ^giite i4 quite fi-«
hiflifed, fold the paper according totte di-^
irifioris thatt have been drawn on It, fb thiif
each of fhedivifioiisS, maty turn one way^
and each of the diviiions O, the other Way f
and paiie the whole on a boai'd, in fudi tf
manner that the folds made on the blank
fide of the piper, may anfwer to the lines
traced in the board. On the paper thus
patftei'fay fomething that may keep it. la
proper form till the pafte is dry. Then
let it be fo placed that ia of its dlvifionk
N a m^y
i8o R A T I O N A L
may be oppofite to each of the pointi o€
view F and G.
To diftinguifh the objeds on the paral-
lelogrank with greater precifibn^ you ihuft
have (as in the foregoing Recreation)' t\Krd
little circles, with a fmall hole in eadb^
and place them exaSly on the points of
view that have been fixed. The eye being
then placed at either of thofe points, will
iifcern the regular figure ; .but when xha
fcheme is viewed in front, it prefents a
form fo diftor ted, that it is impoffible
to cpnjedure what^ it. is inteadcd ta re-
prefent. "'
Obferve, This defign differs in the con-
ftrudlion from that in the firffi Recreation;-
as here, the divifions drawn on the jrregu-
lar figure regulate thofe of the two o^hec
figures. It is indeed more difiicuit,. but
then it is alfb more entertaining ; a&d with
a little application it may be eafily exe-
cuted, as> rtothing more is necefiavy than
'. " ' ■ '■ to
RECREATIONS. i8i
tb transfer the divifions carefully from one
figure to the other.
To perform this fott of anamorphofis
\yith more celerity, you may draw the pfen
0P^ paile^oard, #ind pl^^^Ag » trajpip^rent
paper over jyt, j;race Jh? jTwbjeca tUiiriecya f
^he fam^ gjafteboafd wjU ferve to -eKecutc^
pqually well, ajl fort» q£ fubje^s^.,. ;
JIECREATION XLV.
T^ dm^9 on the h^j^a i:om^ an irregu^
lor figure^ ivhich Jhall appear^ when feen
from a proper point of view ^ not only re*
gular^ but elevated above the furface of
the foney
•• ' ' ' .
npH E geometric method that might be
here given for drawing the * figure
propofed, being extremely tedious and dif-
ficiljt,'^ oh "account of the various curves
that it is^riecelTary'to draw on the bafeoY
the cohe, we fhall Here defcribe 4 more
irmjfle methoii, by making ufe of a lamp.
N 3 This
lit ?RA^^r-Q'M^tf^
drawifig diflc^ed fubje<3:if oa aH-irFCgidar
fythiMty iTfrhatever fhdr %ure tA?Lf he.
LetBFQ (Plate xvn. Fig. i.jbethe
#PMi ott* the bftfis of which;: a drflc^ed
^gttl»i» l» be ,^awn, ^that beirig yiewc^
fi{MD^'tlu^|k)k^ Ijvibfllll apipfia^ it^ari
and eK^6s)y» |elemblH|g tbat ivvbifbr 'ii
ii^eedatNM, ]Piac(e the xofiib in a ci%
-ml?r qTOrfiure^i^^ bdacr^A BCD,
^faidh fliauld^ b^K fiipported |)y four feet^
that the poii^t of thirftone mi^y s^
Ae table on which it ftands. Fix at the
read ofithr board 'an^ uprigi^|Uecel,'1£ha^
ri$ toJ hoM a: MtU-^ cii^l^ 6f})tsi&^' ' throagh
•cisiirhichi&raqde^lkQl^H, of 6«dcf dhth^lof
ytacnch: in /diamfttiQir^ that &siiif Tfort/th^
Bx:cparc 9l lamp as 4, (Fig. 2.) the %h|
:|if wbicji ma^ be raifed bt,l6w£red at J^
|i^e>aodto wbicb is fixal a''bra^..>f^||l
Pl^ hearing a foft^pf funnc| D, in ib^
IhapQ
?RE€1tEATI0NS. iSj
Aape of a .truncatcd.c<niefN and whofe open-
ing at theend nextthe light is not mc^e
4haa three! or four tteths of m inch iii
diameter.
Draw the fubjeft j&a 'would ttpi»*
ftnt <m the bafe of the cone, on a piece of
j^lafs t>f ei0i2d height with ih^ ipacfc M N^,
;diatis,of the kppatent height of the dia-
meter E F, of the bafe of the cone whoa
feen fromilbe^ point H : place it perpen-
dicular on J^e board at the point F| xhat k,
oaittbe extiseoaity of thecone.
Thfcfe lirepara^ioM l>dng made, take
away the piece that hears the point of view
Hyand place the lamp, fo prepared^ in fuch
taatttier fiiat the light may be exadly
^rherdithc point H was. Its rays thto
jMiffing through the glaft at M N, *nfl efa-
^ It . muft. be drawn wltb a fery light ftrofce,
and you fpuil luake uk of a colour that is quite
#paqiic, ^ ^ ^
M " ^ ^ ^ -lighten
1^1 RRAlDIt)/bR^D3 5I
and there fhow^ in a diflortediibrnit^iitbfi:^
fubjeft that is painted on the glaf$.
.. -' f>: . ; . '/ :r .-^^^^
' Thtti draw with a pencil all the ftrcikei
of the thSadtygr thit are on the conftj 8ttdr
takitig «way the light, place the point xi£'
vievtr H^ arid fee if what you have drawn
c0rrcfpottd with the fobjeft on the'glafe,
coitted3dng whac imperfedioi)& there nyay*
chaBce^<to be; rin nhe laft placet <{olonr ^^
fuh^ft fd "traced onthe cone, with Ae ut^ *
moft attention, infpeiQingyoorworkfiklia
time to time from the point of view, be-
fare j^^give iithe finifliing ftrofcesf; . ^
-C' j(\.i r:^..r,:i■ anil :/::■.-. w u^iL ^in^ •-o.-Zy ;
■> WAita. the '%ura that ia^ildrawti ■ and
painted oh f^he i^bafe vf htitsi .cope is
viewed from the point H, it appears to
\)C at the fame point where the glafs MN
was placed, and in the fame form that
it was painted on that glafs. The eye
even perceives it above the furface of
the board in which the cone is placed,
" ^ '^ 7 ?tna
plcafingiilitilliaftr' ^^ • -• /^xii. r;^iT ; .
Note, This manner of drawing diftort^
ed figures bf means of a lapap and.lr4Qi«
piarent glafs, niay be ?idTaiatageQU% ufcd
for tall irregular figures , tjiat ar.et4i&
ficult to draiw geometrically; .Thcflfub..
jefis-tbat are drawn on jthie-gUfs ii^qr
alib/ be- ibaded and, coloured jin. the
iame masiner as for the camera obicuraj
in ordet to have the appearance of cdlqi^C
onthejdiftortedpifiurc^ -ii ' . ■ ^ t-
.•'.;•• ' \ ■ 51 ■ • „ • » '. ■ .• . ■ ' • . • . ' ^ '. •■ ^ . ■ • / »■
If a .qr;Ck ;be def^rib?d, oi>^ jp^ipe^ ;?*:
pafteboard, and^ placed firm upon the ta-
bie, where the cone; is: fuppoftd to bd^it
will have pcepifdy the feme iefi^cd:. . .
"Jr
RECRE-
lU RATIONAL
RECREATION XLVL ^
y^ drato, iofilj mnd correSt^t a I^n^afie
4r any other objeSi, toithotit hing oblige
^4,.t^ o^erve the rulfs .of ftrJ^Sihe^
fin4 viitbovt the aid <f the tmfra. o^-
TIROCyRtt a 1xJ5t of paBetj6aiT9 A BCD
*' (WatcXViLTig. 3.)of abdtit afeot aM
taliidflottg', ilia' iiiadc iit*1ftfe Hape df »
trancated pytfmid, ^ofe 'HafeBDPGU
eight inches wide, upA fix inches higk.
Fix to the othfiiriend <^-it a iulji'of four or
five' in^heihhgriiid *(rfii§h^yWi"tan inw
lOMtfroipL tfie 1b<jx ihore of f)^f«f/ £!!li^'tlie
infide i^^tl^e' bolt i^tH- bli^k fAj^r^ add
place ft u^& f€g df ftatid «f ' wobd H,
*nd ort which it tnay be'ditv^ijfed or depreff-
ed ty the hinge I. '■ -'' ^
Take a fmali frame of wood A B C P
(Fig.4.) and divide it at evelr^ inch by line*
of black :fil|d driw» crbfs it^' forming fof-^
ty-cight
H ft^Q^% i^j t cm s, i$f
pfratglft equad p«rts ; <£vide theC^ into flal}
^mal^en tii^pl pftrtBr bf linis^iffiAer fiUc * f
fix this fiame 9t the ^end BI^ as the li^fc
^f the pyramid. ^ ^
Fravidi^adrawkig paper, ^vided ihtQ
:^ iii^^ nuiiib^r df parts ati is the Irktoie,
]>7 lines lightly drawn in. chaUc:. It it
fipn^xc^i .^^y^ 4«p«i^(^ eatirdty. m ^
fjzc you/prppo<e |t)>. dra^^ olue^ hy
^tMf i<»%ttm€?»t, .
{, . Plf0 tibjif ihkfltt^^ .(^pofite a }a|id^
^tfifeji or.w^' G^htr oi)}e^ th&t yi99,<vi^
:fb»^dniw^ aad^^ thjC leg §rm3y op, pr in
Ihe gfcii9iM^,::!tj^ it may not ^abe r tht^
jtiiming it to the fide yO» 5:hpoife| raif«i^ of
Ipdipe it» jU|d put the tubp luitbex.in (^
put, till you have gained an ^dvanta^eoiui
jriew of the pbjedt you intend to draw.
.. f The dif^c^iitfize of the ,filk ferves tp diilipr
euiib fflote readily the correfpoiidioe divifion^.
; -. '-. ■ i Place
i^o RATI 6 N A t ,
the opening to which EFGH, ihould be^
.a little lefs than the print. Cover thitf
opening with a glafs, and paint all thd^
^ace between it ancf the prihtSy which
(hpuld be about two (x* three inchedyblael|;
The frajBe that contains the ftiy fhoul^
be about an inch behmd th£ othett Iti
t^e back part of this box» which is behind
die printSf and which may be about foiff
inches deep, place four or fiye fmalf
candltsfUcks to hdkl wax lights, and coyer'
that part entirely with tin, that i| may b9
the more himmouSb
When iht j^tiot is placed betweenrthJ^
wax lights and the opening in. the front of
the hoxy and there is no otha:' light in the
room, the eflFedl will be highly pleafingr
efpecially if the lights are at a fufiicient
difiknce from each others and not toa.
ibong,^ that they may -not occafion any
1>lots in the print. Thofe prints that re-
prefent tl\e riiing of. letting of the fun
will have a very pi^lurefi^ue appearance.
Such
if ^> /: O t ihyi
. f : • ..
-.t:
fi^!'.
;:^"
^ J T
:-ti. /-ivi;^ :!07 jjuiiT ,}^:;>^:^ :;t!5rxt»T J^ji^rqj^rfi
: .:Ai'if :': nn'v'^ ,;.:: ^ ?/. ;;:xi£'1l; -jioo lliiw
^*'' ^fhc? ::*:•' ..- li'o'oj iiuU K? c;
T
:;•> iiCiiX-.-itj'../! •■,
. :::aq 3ii: iv
^/.ih
'-■■ V'.'- -•• ■• ■''•i'i c- ' ■
i
1
I
1
t
1
O'vJC
KZQVLtAtiQUB. 191
SQthM rcprefent conflagratMMM have alli9^
Note. There ihouldl^ two greovw for
Ike prkit next the glafsi that you inay ia>-
felt af fecond fubjed befoM you draw away
the firft : and that the lights in the back
idf the box may not be diicoTered.^
You muftnot, thinking to make the
print more tranfparent, [cover it with.
Taumifh} for that will prevent the degra-
datioa of the colours fsom being vlfible.
The frame fhould enter the (ide of the box
]by a groove, that a variety of fubjeAs may
be, introduced,
RECREATION XLVm,
tranfparent illuminations.
^yEboxtbatistoeoclofe thcfe fubje<as
may be made in the fame manner with
lliat of the preceding Recreation, only
obferving that it will be proper to aug-
meat
i^a RATI OK A t
HDnit the number of lights, and employ
fuch prints as are agreeable to the fubje£t#
With a very fmall circular tool you arc
to cut out all the phces where the light is
intended to appear, or where it is expreflf-
edy if the print reprefent an illumination*
Particular care muft be had to make ufe
of the fineft tools in thofe parts of the print
that are intended to appear at the greateft
diftance.
Thefc prints muft by no means be tranf^
parent, like thofe in the preceding Recre-
ation; on the contrary, they ftiould be
printed on a thick paper, or rather it
fliould be doubled, that very little of the
engraving may appear* Behind the print
muft be placed a very fine tranfparent pa-
per, varniihed, fixed on a frame, and
lightly painted with a deep yellow, or
faffron colour, which muft be laid on thick-
eft at thofe places that are oppofite the
parts of the print that are to appear at tbc
greateft diftance*
The
\1&fgfat icene, may be very pleafing^y j-e-
^^j^wiented m tliis method. ' Vhus?procurd
^ a Un^%jpp» io which is t^ .^g^rfi'Uf the
fe^ipg fun^ illuminate^ fts ftboye ^f<«ib-i
. ed. Let the bottoni, of .jhi$ fceii« >.i^ft
Upon an-ui?right board m. the toxf^-of
. about two three inqhbs high» apd Jfttitbe
,^gradi»aUy flaoyed off th^^bow^ia^ii^lp.w-
;• ierqd .dwft to the bottojft 42|f;di<;^boji|^pn
the ifide next the glafs, by whklriftefens
the fun will appear to defcend. Let the
.:ii^ht«i;ilMsh(\begt^ttal!ya^hli^ and
>hange^tlt» &ti^ landicap^ £tt- Jt4iig)H ^foe^^
^» iwitbthe mcKm kndflaf9y.ptd|)er!y ftetfeirttt*-
y ed* 'Th^ yellow:; pap^ muil^beJigft8ifgied
Jk^t oQetha|^8. white ,ited^trahfp*etM^iihd
: th^ lighta. be agaia-in^po^fc^Be^^^J|dte
:;^he mc^Ur ftatsi and <)ther'ilkftnMSa%ed
I parts will ^appeai- i* theit' natural ^An,
: For -the jiit>re edfy i^tndrting^ ^oT^^
-lightKlHey miy; be all placed '^upotireyne
1 Jftandi but at,different dil^nceBi * ''^ -^^
Vou It*
o) *-*:^- : .. :'--y - '■' ^-^^'--^
:i'^-?«^
^T^is
.194 , flL.^,i:iON AhL,
This piece of illumination might alfo?
be put into the common opticaj machine ;
but the inagnifying glafs there ufed con-
i^derably c^cging the objedle^ thiie liiht
refle^ed by the -cut and tramfparcnt parts,
tben^ becomes greatly weakened, as 'it takes
up a imuch larger fpace^ s^Bid thait gi?eatl^
diminiflieS' the vivadty ^hich is tiecd&fry
jto iimtate nature^ ^id to produce the iltu^
fion,-. If, however, you are diefirous of
viewing this piece by the magnifier^ jou
muft take away the inclined mirror which
is placed in thofe fort of optical machines,
and, place the tranlparent pidyore or print
in the front of the glafs; pth?rwffc it,wiH
be fcarce poffibJe tfx render , it . luminous^
except by reflexion, which; affords. but :a.
very feebjjs. light*. *
ACOUS-
JEl^CRfeAtldNS. 1^5
AC O U S T I C S.
^ I ''HE fciewc of acouftics inftf ui^s us ixi
the natute of found. It is divided
by fome writers into diacouftics, which ex-
plains the properties of thofe founds that
come diredly from the fonorous body tO
the ear ; and catacouftics, which treats of
refleded founds : but fuch diftindion does
not appear to be of any real utility^
. 1) E F t N 1 T r Q N S.
i^ Solinds are either acute or grave^
fimple or compound.
2. Thofe founds that are fhrill or fharp
are called acute: and
3. Thofe that are deep ot hollow, ate
Called grave founds.
4. A finiple found is that produced by 3L
fingle ftroke on a fonorous body; and
compound founds ard thofe that proceed
from feveral bodies ftruck at the fame time,
or from feveral ftrokes on different partd
of the fame body.
O 2 5. A
196 R AT I O I^ A t
$. A cKbffl 18' a ftriAg 6f 'catgit, brafsv
wir^, &c. faftretched as when ftruck tcy
yield a diftindl found.
6. A vibration re the regular, alternate*
iiaotron of bodies, by whrch,^ when put
out of their natural ftate, th?y endeavour
to retwrri to it. Thus the ftring A B (PL
X VIIl. Fig, I . b^ng ferccd out of its haturat
poiition to that of A c B, vibrates to J, and
then to fjfjgy &c» till it returns to its firft
ftate at AB^
A P H O R r S M S-
J. All founrf is produced by an undulaf-
tory or wavelike^ motion^ of the air *, ex-'
cited by the vibrations of a fonorous bo-^
dy, proceeding from a ftroke of fome'
other body,
2. Acute founds arife from q^uicfc vibfa-*^
^ Th^t air is the medium of found is evident
firom a bell placed in the receiver of an air-pump,
virhich may be heard to a confiderable diftance be-
fore the air is exhaufted, but after, can fcarce ht'
<iiftii>giii(ked when quite near.
tion^
RECREATIONS* 197
dons of the parts of a body, and grave
founds :froin flow vibrations.
3. Smooth and dear fourids proceed
from bodies that are homogeneous, and
of an unifarm figure ; and harfli or ob»-
jtufe founds, from fuch as are of ^ mixed
matter and irregular figure, -
4, In bodied of a fimila^r figm^e and diroen-
fion, and of equal elafticity, their tones are
^n proportion to their denfities : the den-
ser the body the graver is the tone; there^
fore a bar of gold muft have a graver
foun^ than one of filver, of equal dimen-
fions ; jfuppoiin^ them to be of equal elafr
ticity. ' \
5, if two bodies are compofed of the
fame matter, and arie gf fimilar figure,
their tones vvill be in propoftion to the
quantities of matter. Thus, the tones of
two globe of brafs will bjClfo each other in
l^roportidh to their diameteirij,
., ; .6. The vibrations of, chords Is in pro-
portion to their length3i diameters,' and
teafion.
O 3 7, All
198 RATIONAL: >/
7. All the vibrations of the fame chordf
as AcB, (Plate XVIII. Fig. j.) AdB^
A^B, &c. are made in the fame tkne*
8. If two chords are of the fame diamo^
ter or thicknefs, and equally ftretched,
their vibrations, in the fame time, will be in
proportion to their lengths inverfely, that
is, a chord of fix inches will make two
vibrations while a chord of twelve inches
makes one*. ';
9. If two chords frequently vibrate to^
gether they produce a concord ; arid the
more frequent the coincidence of vibration,
the more pleafing the concord.
10. Sound is propagated in concentric
* From hence we learn how to divide atiy
chord fo that it may found the feven concords ^ as
thus, divide tl^e line A B (Plate XY.III. Fig. 2.)
into tu'o equal parts in C, and C B into two equal
parts at D, and C D into two equal parts at E.
Then A C will be to A B as f, that is, an oflave,
AC to A D as 4, a fifth : AD to A B as |, a
fourth. AC to A E as ^, a third greater. AE
to A D as -^, a third lefTer. E B to A E as 4, a
fixth greater, and A E to A B as 4> a fixth Icflfer.
circles
REtJUEATPoWg. %
fdrcl€8> every way touiid the " i&iiorQus
ibody*. / •• ^" ' ' ■-■''■' ' ^'^ '^
1 1. AH founds, whether great €^ ftikaUy
are of equai velocity. n-
IS. The fpace paffed ovef by found is
Gonftantly equalin equal timesi WhfetHer if
come from a greater or left diftarice;- ^
1 3. The motion of found is at the^rate
6f 1 142 feet in a fecond, and ho <AftatIes
obftruQ: its progrefs ; a contrary - Wind
only a fmall matter diminifhing it^ velo-
.cityf. -• '•= 'i ^ ■^' T^riTv;
* The dlftance to which founds may be heard
is very great. Authors of credit relate tliat till
found of cannon has been .hear<ct>kSa"aiKp '200
miles.
f By this axiom we are enabled tofind the dift^ncc
between objefts that would be otherwifc immea-
furable. For example, fuppofe you fee the flafli
of a gun in the night at fea, and tell feven feconds
before you hear the report, it follows ^therefore,
that the diftance is feven times 114.2 feet^ that is
twenty-four yards more than a mile and a half.
In like manner if you obferve the number of fe-
conds between the lightning and the report oi the
thunder, you know the diftance of the cloud frqia
whence it proceeds.
O4 14. The
20P: ft; h T 'I QM A J4 1 :a
14. The velocity of fouad i% to that of.
a brilk wind as fifty to one* ( st
15. The flreagth of founds i$ greateft
in cold and denfe air^ and leail in that
which i3 warm and rarefied.
i6« In all founds the angle of incidence
is equal to that of reflexion, thut iSi if a
line be ilrawn perpendicular to the refleft*
ing furface, the point from which the
found iffucs, and that to which it is re*
fleded, will be equally diftant from the
perpendicular line.
RECRE-
R ElCH eat I O N S. api
RECREATION 2^IX.
A N jaeo|ipi|g is a fmall globe of brafs or
. other w^i, into which a flender neck
or pipe ia iu%rte(t : Thia ball, when made
red hoty i& caft into a veffel of water,
which will ruflx into its cavity, then
almoft void Qf air. The ball being then
fet on the fire, the water, by the rarefac-
tion of the internal air, will be forced out
m.fteam, by fits, with great violence, and
'with a ftrange noife.
If to the necks of two or more of thefe
scolipile? there be fitted thofe calls that are
ijfed by fowlers and hunters, and the aeoli-
piles be then placed privately on the fire; as
the fteam rufhes forth they will make fuch
a horrible noife, that a perfon who is ig-
norant of the contrivance cannot fail being
greatly aftonilhed.
, - ^ - Great
Great care Ihould be taken that the neck
of the^^eioUpile ^\)t not flopj^d when4t is
placed on the fire, for in that cafe it would
burft, and might do no fmall mifchief.
RECREATION L.
TAe communicative bujis.
¥ ET there be two heads of plafter of
Paris, placed on pedeftals, on the op-
polite fides of a room. There muft be a
tin tube of an inch diahieter, that muft
pafe from the ear of one headv through the
pedeftal, under the floor, and go up to
the mouth of the other. Obferve, that the
end of the tube which is next the ear of
the one head, fliould be confiderably lar--
ger than that end which comes to the
mouth of the other. Let the whole be fo
difpofed that there may not be the leaft
fufpicion of a communication.
Now, when a perfon (peaks, quite low,
into the ear of one bull, the found is re-
verber-
RECREATIONS. 20^
^berated through die kngdic^ the tidie,
and 179111 be diftmffly heard hj anyone
nvho fiiall place his ear to die mouth of the
other. It is not neceflarjr that the tube
fhould come to the lips of the baft. If
there be two tqbes, one going to dieear,
and the other to the mouth of each head^
two peribns may converfe together, by
applying their mouth and ear reciprocally
to the mouth and ear of die bufis ; and at
the fame time odier perfims that fland in
the middle of the chamber, between the
heads, will not hear any part of their con-
Verfation.
RECREATION U.
TAe oracular head.
OLACE a buft on a pedefbd in die cor-
ner of a room, and let there be two
tubes, a9 in the foregoing Recreation, one
of which muft go from the mouth and the
pther from the ear of the buft, through
the pedeftal, and the floor, to an under a-
partment.
'• ■' ' ' '^ ^ ' ; ;i '; 1 'A'
2P4 R A T I: O W-A.iLn.i:rr..
partment. There may te like^ife wirt*
that go from the under j^w,; aiiid &e eyes
of the buft, by which they miy be eafily
moved.
A J)erfon being placed in the undcff
room> and at a fignal given applying his
ear to one of the tubes, y^ill hear any
queflion that i^ aflced; ^q4 immediately
reply, moving at the fame time the mouth
and the eyes of the buft^ by nieans of the
wires^
. .RECREATION Hl.^
A folar Jonata^f .
"tN &* large cafeVifuch as is ufcd for dials
and- fpring; cltkks, thefi*oiit of wliich,
w-it4eaft the lower part of it, muft be of
^fefe^^dvcff ed on the mfide with gaiizeV let
th^ 4>e placed a barrel organ, which,
whefi%6urid-upi is preyentedfrom play-
ing, by a catch thitt takes a toothed wheel
At the end of the barrel. To one^ end of
this
kfiC^EAtlONS. 26^
-this catch A^^ifeiift B^ joined a wire^ at
the end. of which there i& a flat circle of
cork, of the faipe dimenfion wiii the ix^.
fide of a glafe tubevin which it is to rife
and fall. This tube muft commu|up2^te
with a refervoir that goes aerofe the front
part of tb? bottom of the cafe,_ivfrhtc}i id to
be filled wkh XpirilSy liich as istifediti
thermoineter$> but tiot -coleurcd, that it
may be the^ better concealed by the gajuice.
This c>fe being placed in the fiiiii the
fpirits wiUbe rarified by the heat, and rif*
ing in the tube, will lift up the catch or
trigger, and fet the organ in play y^- which
it will continue to do as long aa it is kept
in the fun; fot the fpifits cannot run out
of the t|i}^3, that part of the. catch to: whi<t>^
thq circle |s^ ^jced being preyejnte^. fjroA
fiftng b^^ypnd a certain point, jby.a cl^eck
placed oyef. it Care muft be takefcto c^move*
the maQhiiji^g.put of the fun/ before the oi»gan
runs dpwq, that its flopping may r^b^, evir
dently eflFea(^d,by the 6g|d.: . . . m ; . ^
7 . When
2o6 KiAT I ON At:
When the machine is placed againf^ tte
fide of a: room on which the fun fhines
ftrong, it may conflantly remain in the
fame place, if you enclofe it in a fccond
cafe, made of thick wood^ and placeti latm
little diftance from the other. . .When f6u
want it to perform, it, will be only neceflfiM^
to throw open the door of thG^outi^r cafyj
and expofe it to the fun,.
But if the machine be moveable, it wiJI
perform in all feafons by being placejJ ber-
fore the fire; and in the winter it. will
more readily flop when removed into the
cold. . .
A machine of this fort Is faid to havfe
been invented by Cornelius Dreble, in the
laft century. What the conftrudtion of
that was we know not ; it might' very
likely be more complex, but could fcarcc
anfwer the intention more readilyf
RECRE-
RlZ/CIt E> A T lO N? S. ^7
.^ iH E CR E A T I ON LIII.
^ . . -^f? mtomatous harpjcfiard.
T TN I>B R the keys of a common harp»-
ficfhbrd Idt there be fixed a barrel,
fottiethitig like' that in a lelianiber organ,
Wkh-ftop^ or pins correfpotiding to the
tunes you would have it play. Thefe
flops muft be moveable, fo that the tunes
may be varied at pleafure. From each of
the keys let there go a wire perpendicular
^owri \ the ends of thefe ivires mufl: be turn-
ed up for abbut one-fourth of an inch. Be-
hind thefe wires let there be an iron bar,
to prevent them from going too far back.
NoW, as the barrfel turns round, its pins
take the ends of the wires, which pull
down the keys, and play the harpfichdrd.
The barrel and wires are to be all enclofed
in a cafe.
In the chimney of the lame room where
^he harpfichord ftands, or at leaft in one
adja-
20^ RATIONAL
adjacent, there muft be at fmoke jack,^
from whence comes down a wire, of cord,-
that paffirig behind the wainfcot adjoiri-:
ing the chimney, goes under the floor, and
tip one of the legs of the harpfichord, into
the cafe, and round a fma)l wheel fixed oil
the axis of that firft mentioned. There
fhould be pullies at different diftanced, be-
hind the wainfcot and under the floo^, to'
facilitate the motion df the chord.
This machinery may be applied to any
other keyed inftrument, as well as to'
thimes, and to many other purpofes wher6'
a regulair continued motion is. required.
An inftrument of this fort may be con-
fidered as a perpetual motion, according to'
the common acceptation of the term, for it
will never ceafe going till the fife be extiir-
guiffied, or feme parts of the machinery be
worn out.
R E C R E-
RE OR E AT I O N LW.
ji^entojalfymphony^
* j\ T "tlie toji of a rumfner-houfe, or btlier
* ^ bulldirtg, let tliere be fixbd a vane AB
(jfPl. tViri-i^ig. >)on which is the pinion '
C, that takes the toothed wheel D', fixed on
the akis E F, w'hich /at its other end carries
the wheel G, that takes the pinion H. All
^thefe wheels and pinions are to be between
*he roof and the cieling of the building.
Xhe pinion H is fixed to the perpendicu-
iar a^^is iK, y/hich goes dawn very near
the w^ail of the room, and may -be^eovered
after the fame manner aa are bell-wires.
At the lower end of the^xisJK there is a
foiall pinion L, that takes the wheel Mj^
fi^ed on the , axis of the great wheel N Q,
fo this wheel tliere muft be placed a num-
ber of flops, correfponding to the ;:unes
it is to play, Thefe flops are to be move-
able, that the tunes may be altered at plea-
sure. Againft this wheel there mufl hang
Vol. 11. * P twelve
210 , RATIONAL.
twelve fmall bells, anfwering to the notea
of the gamut. Therefore, as the wheel
turns round, the flops ftriking againft the
bells, play thefeveral tunes. There fhould
be a fly to the great wheel, to regulate its
motion when the wind is ftrong. The
wheel N O, and the bells are to be englofed
in a cafe.
There may be feveral fets of bells, one
of which may anfwer to the tenor, another
to the treble, and a third to the bafe ; or
they may play diflFerent tunes, according to
the fize of the wheel. As the bells are
fmall, if they are of filver, their tone will
be the more pleafing,
Inftead of bells, glalTes may be here
ufed, fo difpofed as to move freely at
the ftroke of the flops. This machinery
may likewife be applied to a barrel-organ 5
and tp many other ufe$^
RECRE^
RECREATIONS. 2U
RECREATION LV.
^he noSiurnal reveilleur.
A GAINST the wall of a room, near the
deling, fix a wheel of 12 or 18
inches diameter ; on the rim of which
place a number of bells in tune, and, if
you pleafe, of different fizes. To the axis
of this wheel there fhould be fixed a
fly, to regulate its motion; and round
the circumference there muft be wound
a rope, to the end of which is hung a
weights
Near to the wheel let a fland be fixed,
on which is an upright piece that holds a
balance or moveable lever, on one end of
which refts the weight juft mentioned, and
to the other end muft hang an inverted
hollow cone, or funnel, the aperture of
which is very fmall. This cone muft be
graduated on the infide, that the faad put
P 2 io
212 RATI ON A L
in may anfwer to the number of hours it
is to run. Again H: the upright piece, on
the fide next the cone, there muft be f\xed
a check, to prevent it from defcending.
This ftand, together with the wheel, may
be enclofed in a cafe, and fo contrived as
to be moved from one room to another
with very little trouble*
It is evident from the conftrudion of
this machine, that when -a certain quan-
tity of the fand is run out, the weight will
defcend, and put the wheel in motion,
which motion will continue till the weight
comes to the ground. If the wheel be re-
quired to continue longer in motion, two
or more pullies may be added, over which
the rope may run.
The fize of the bells fhould be adapted
to the fomniferous difpofition of the party
they are intended to rouze; or, if you
pleafe, a drum or t^bor may be added,
the
RECREATIONS- 213
tlie ftick to which may be fixed in the fide
of the room, by afwivel that goes through
the middle of it ; and one end of it being
lifted up by teeth placed on the circum-
ference of the wheel, the other end will
alternately ftrike the drum.
P 3 RECRE-
114 R A t I O K A t
RECREATION LVI.
A mufical cafcade.
'^IXTHERE there is a tiatural cafcadef^
near the lower ftream, but not in
It, kt there be placed a large wheel, equal
to the breadth of the cafcade r the diameter
of this wheel, for about a foot from each
end, muft be much lefs than th2tt of the
middle part; and. all the water from the
cafcade muft be made to fall on the
cnd^ ♦. The remaining part of the wheelv
which is to be kept free from the water^
muft Gonfift of bars, on which are placed
ftops, that ftrike againft bells, as in the
54th Recreation : thefe ftops muft likewife
be moveable, but larger than in that Re-
creation, as well as the bells, that they may
be heard much further. It is evident
♦ The water that falls on the wheel may pafs thro*^
pipes, io that part of it may be made occafionally
to pafs over or fall fhort of the wheel, as you would
Irave the time of tb« mufic quicker or flower.
from
Recreations, us
fjrom the conftrudion of this machine, that
the water falling on the floats at the ends
of the wheel, will make the flops, which
are adapted to different turves, flrike the
notes of thofe tunes on the refpedive bells.
Two or three fets of bells may here be^
placed on the fame line, when the cafcade
is fufficiently wide.
Where there is not a natural cafcade,
one may be artificially conflru£ted, by raif-
ing part of the ground, wherever there is
a defcent of water ; whether it be a ftream
that fupplies a refervoir or fountain, or
ferves domeflic ufes ; or if it be refufe wa-
ter that has already ferved fome other pur-
pofe.
P 4 R E C R E-
»i6 R ATI on A t^
w
RECREATION LVIL
Reverberated founds.
COUND, like light, after it hw been rc^--
fleded from feveral phces, may be'
xsolleded in one point, as into a focus ;.
and it will be there more audibly than in«
any other part, even than at the place from
whence it proceeded. On this principle'
it is that a whifpering gallery is con-^
ftruded..
The form of this gallery muft be that of ar
concave hemifpher^ *, as ABG (PI. XVIII..
Fig. 4.) and if a low found or whifper be
uttered at A, the vibrations expanding;
themfelves every way will impinge oa-
the points D D D, &c. and from thence be^
reflecled to E E E, and from thence to the
points F and G, till at laft they all meiet
* A cylindric or elliptic arch will anfwer ftill
better than one that is circular.
RECREATIONS. 217
in C, where, as we have faid, the found
will be the moft diftin^ly heard*
Upon tills principle alfo it is that the
fpeaking trumpet is formed. For the found,
in pafEng through the long and narrow
]part of the tube, is continually refleded
from its curved fide into the axis, and by
that mean is prevented from fpreading till
at its exit from the tube, whereby the
ffrength of the found is greatly increafed.
As by the laft aphorifm, page 200, the
angle of refledled found is equal to that
of its incidence, if we know the point
from which any found proceeds, and the
place from which it is refledted, we may
eafily find the point in which its echo will
be heard.
To hear the echo of one fyllable, we
muft be at the diftance of 120 feet from
the refleding furface : for two fyllables,
240 feet; for three fyllables 360 feet, &c*
For
220 RATIONAL
RECREATION LVIlt.
The converfive Jiatue.
pLACE a concave mirror of about fw©
^ feet diameter, as A B * (Plate XVni-
Fig. 5.) in a perpendicular direditon. 'The
focus of this mirrror may be at 1 5 or 1 8
inches diftance from its furface. At the
diftance of about five or fix feet let there
be a partition, in which there is an open^
ing E F, equal to the fize of the mirror ;
againft this opening muft^ be placed a
pidure, painted in water-colours, on 1^
thin cloth, that the found may eafily pafa
through it f.
* Both the mirrors here ufed may be of tin or
gilt pafteboard, this experiment not requiring fuch
as are very accuratei
f A Recreation of this kind may be performed
in a field or garden, between two hedges, in one
of which the mirror A B may be placed, and in
the other an opening artfully contrived. The
more effeflually to conceal the caufe of this
illufion.
RECREATIONS. 221
Behin4 the partition, at the diftance of
two or three feet, place another mirror
G H, of the fame fize as the former, and
let it be diametrically oppofite to it.
At the point C let there be placed the
figure of a man feated on a, pedeftal,
and let his ear be placed exadly in the
focus of the firft mirror ; his lower jaw
muft be made to open by a wire, and fhut
by a fpring ; and there may be another
wire to move the eyes ; thefe wires muft
pafs through the figure, go under the
floor, and come up behind the par-
tition.
Let a perfon, properly inftrufted, be
placed behind the partition near the mir-
ror. You then propofe to any one to
fpcak foftly to the ftatue, by putting his
illufion, the mirror AB may be fixed in the wain-
fcot, and a gauze, or any other thin covering,,
thrown over it, as that will not i^ the.leaft prevent
tbe fpu^id from being reflected,
mouth
122 RATION A L
mouth to the ear of it, affuringhim that it
*will anfwer inftantly. You then give
the fignal to the perfon behind the par-
tition, who, by placing his ear to the
focus I, of the mirror G H, will hear
diftindly what the other faid, and mov-
ing the jaw and eyes of the ftatue, by
the wires, will return an anfwer diredly,
which will, in like manner be diftiridlly
heard by the firft fpcaken
Remark. This Recreatien appears to be
taken from the Century of Inventions of the
Marquis of Worcefter ; one of tbofe men of
fublime genius, who are able to perform
adions infinitely fuperior to the capacity,
or even the comprebenfion, of the mere
fcholar or man of bufinefs ; and though
his defigns, at the time they were pub-
liflied, were treated with ridicule and
negleft, by the great and little vulgar,
who, judging by their own abilities, are
ever ready to condemn what they cannot
com-
PlATEXVlII,
J^/.X^/s^^^
^
T--^:::
^'-C^--^ ^^'-^'C^"
B
c jp J>
D
RECREATIONS. 223
compehend, yet they are now known to
be generally, if not unlverfally, pradi-
cable. The words of the Marquis 2^re
thefe. " How to make a brazen or ftone
head, in the midft of a great field or
garden, fo artificial and natural, that^
though a man fpeak never fo foftly, and
even whifper into the ear thereof, it will
prefently open its mouth, ^nd refolv? the
queftion in French, Latin, Welch, Irifh, or
Englifh, in good terms, uttering it out of
its mouth, and then fhut it until the next
queftion be alked.**
RECREATION LIX.
ybe Orgafif
npHE recreation this Inftrijment affords
is known to every one ; but what
^we here propofe is a defcription of the
feveral parts of this moft noble and com-
prehenfive of all mufical machines, and of
the manlier by which its numerous founds
arQ
224 RAT I O N'A'L '
are pr odiMied : and fuch a ddcf iption wiU^
perhaps, afford a perfon of ant ingenious
difpolition a recreation little inferior* ta
the founds tbemfelves. . v - :
There are various forts of organs, but
that we fhall here defcribe is the grand,
or church organ, which confifts of two
parts, the main body, called the great or-
gan, and the pofitive or little organ, which
forms a fmall cafe or buffet, commonly
placed before the great organ, ^The fizc
of an organ is generally expreffed by the
length of its large ft pipe : thus they fay,
an organ of 8, 16, 32 feet, Sfc.*
The feveral parts of the church organ
are as follow : H I H (Plate XIX, Fig. !.•),
is the found board, which is compofed of
two parts, the upper board or cover H H Hj>
• The organ in the cathedral church at tJlrrt/
in Germany, is 9.3 feet high, ^nd 28 broad i;-.it*
%S?^J^'P^ ^s ^3 inches diameter, and it ha^ 16
pair of bellows.
and
REGREATIONJS. 225
and the under board H I, which Is much
thicker than the other ; each of thefe con-
Cfts of feveral planks, laid with their edges
to each other, and joined very clofe toge-
ther. In the under fide of the lower
board there are made feveral channels^
which run in the diredtion L L, MM,
&c. and ar6 continued as far as there are
fiops in the organ, and come almoft to the
edge H K. Thefe channels are covered
over, very clofe, with parchment or leather,
all the way, except a hole that is com-
monly at the fore end next H K, upon
which a valve or puff is placed. Thefe
chatiiiels are called partitions. When
this valve or flap is fhut it keeps out the
air, and admits it when open. On the
upper fide of the lower board there are
likewifc cut feveral broad, fquare chan-
, nels, lying crofs the former, but not {b
deep as to reach them ; thefe lie in the
diredion LN, PQ^ &c. To fit thefe
channels there are the fame number oiF
Vol. !!• Q^ wooden
226 RATIONAL
^oodto iliders or regiftcrs yj yj j^ &c
running the whole length ; and theie may
be drawn out, or thruft in,, at pkafure.
The number of thefe k the iameaathat of
tiie fk>ps in the organ.
. tKKK is the wind cheift, which is a
fquare box, fitted clofe to the under fide
of the lower board, and made air tight^
io that no air can get out, but what goes
through the valves, along the partitions.
VV are the valves or pufFs, which
©pen into the wind-cheft; they are all
inclofed in it, and may be placed in any
part of it, as occafion fhall require. One
of thefe valves, with the fpring that {huts
it, and- the wire that opens, it, is repreferit-^
cd by Fig. 2.
C, D, E,F, &c. are the keys on which
the fingers are placed, when the organ i&
j^layec^^: thefe keys lie over the horizcmtal
'bair
tar of wood W, in which are ftuck art
fequal number of wire pinfc Zj Zj oh which
keys are fixed j and the keys move u|j
and down on the bar^ as on a centen
There is another bar, againft which thd
keys fall when put down, and which is
here marked 3 : on this alfo are feveral
1«riredi whith go through the keys, to
guide them ; atxd on this bar a lift is faften^
C(J to hinder the keys from knocking a-^
gainft the wood;
The keys are made to comtniinicatd
with the valVes fevetal ways, as we fhall
faow defcribci Firft^ j, Si s^ are the key'
foUers, ihovihg on the pivots /, t : theft
rollers lie horizdntailly, one above another^
ind ate of filch a lerigth as to reach froiEl
the Valve to the key : a^ a^ a^ are arms or
levers fixed to the key-rollers i w, wj the
talve wires fixed to the atrmS ^, a^ and tc*
* Valves V^ and go throhgh the holes >4, hi
in the bottom of the wlQ^-ejbiefl: : bi by hi
Q^ are
228 RATIONAL
arc likeWifc arilid fixed to the key- rollers 1
d^ d^ dy the key-wires, fixed to the arms
by 6 J and to the keys C,D, E. Now whea
the end of any one of the keys C, Di E, is
put down, it pulls down the arm 6j by the
wire //, which turns about the roller s with
the arm a, that pulls down the wire w^
which opens the valve, that is fhutby the
fpring as foon as the preflure is taken oflF
the key. In this conftrudtion there muft
be a wofm fpring fattened to the key, and
to the bar W, on the further fide, to keep
down the end ^, of the key.
Another method pf opening the valves
is thus. : xyy xy^ are flender levers, move-
able on the centers i, i : 5 ;c, 5 :v, are wires
going from the further ends of the keys
to the ends x of the levers : ^ V, j^ V, are
other wires, reaching from the ends^ of
the levers, through the holes ^, to the
valves V. So that- putting down the key
C, D, &c, raifes the end^j, which thrufts
S ■ ^ • up
/
RECREATIONS, 2*9
up the end x of the lever, by the wire -
^x; this depreffes the end x of the lever,
which pulls down the wire^Vi and opens
the valve V,
A third way of opening the valves is
this : at the end of the key i, is a lev^r
8, 9, moving in the center 7, This mak^s,
with the key, a compound lever. From
the end I9, a wire goes to the valve. Now
the putting down the end 6 of the key,
raifes the end 8, which depreffes the end.
9, of the lever 8, 9, pulls down the wire,
and opens the valve. There is only one of
thefe drawn in the fcheme, and but a few
of the others ; to avoid confufion,
R, R, are the rollers, to move the fliders>
by help of the arms cf^ cf, which s^re
fixed horizontally in thefe rollers \ k e^k e^
are alfo levers fixed in the rollers ; le, le^
are the handles, which lie horizontally,
and pafs through th© holes /, / ; they ar^
(^3 fafteqcd
*3d RATIONAL
faftettcd to the lever ke, ^ing inovcabl*
jibbut a joint at ir.
Now, any handle I p^ being draWii o\x%^
pulls the end e toward /, which turns a-^
^lout R>t, along with the arm cf\ and th?
end /pulls out the Aider /g" ; 4nd \^hen f
18 thrullin, the arm ^yiikewif? thruftslq
the flider/^^
Upon the fcvcral rows of holtes whic^
itp^zx 6n the top of the upper board,
there are fet up an equal number of rowi^
^ pipes* The pipes 6£ ?tn organ are of
^Wo kinds, the oftch^s a mouth like k flute,
the other with reeds. The fii»ft, c^lle^-
pipes of mutation, poqfift (i.) of ^ fop|
A ABB (Fig/ 3.)Vhichi8alioIlowcoxie,
that receives the wind that is to feiuil^
the pipe: (2.) to this footis faftexlcd <Ke
|)ody of the pipe B B D D. Bett^ieft thfe
foot and the body of the pipe is a dia-
- jfhfagin or partition FE f, that has a \6tt^
• hut
R5€REATI0NS. 231
l>iit njirrow aperture, by which the wind
comes out : ovef this aperture is the mouth
BBC, whofe upper lip C, being level, cuti
the wiad as it comes out.
The pipes are of pewter ; of lead mix-
4ed witha twelfth part of tin, and of wockL
Thofe of pewter are always open at their
extremities : their diameter is very fmall,
and their found very clear and flirill.
Thofe of lead mixed with tin are larger^
the fliorteft are open, the longeft quite
ftopped : thofe of a mean fize are partly
fiopped, and have befide a little ear on each
fide the mouth, to be drawn cJofer or fet
further afundcr, in order to raiife ot lower
the found. ^ The wooden pipes are %aare,
and their extremity is ftopped with a valve
or tampion of leather. The found of the
wooden and leaden pipes is very foft^ the
large ones ftopped are4:ommonly of wood^
the fmall ones of lead. The longeft pipes
give the grave ft found, and the fliorteft
the moft acute : their lengths and widths
0^4 *re
23^ RATIO N A L
arc determined by a fixed proportion to
their founds, and their diviiions arc regu-
lated by a rule, which is called the diapa-
fon. The longeft has commonly fixteen
feet; but in very large organs it has thir-
ty-two feet. The pedal tubesf are always
open, though made of wood and of lead*
Whatever note aily open pipe founds,when
its mouth is flopped, it will found an oc-
tave lower ; and a pipe of twice its capa^
city will likewife found an oilave lower,
A reed pipe confifts of a foot A A BB,
(Fig, 4.) that carries the wind into the
fhalot or reed C D, which is a hollow de-
mi-cylinder, fitted, at its extremity D, into
a fort of mould, by a wooden tampion G.
The fhallot is covered with a plate of cop-
per K K L Lf fitted, at its extremity I I,
into the mould, by the fame wooden tam-
pion. Its other extremity K K, is at liber-
ty, fo that the air entering the fhallot
makes it tremble, or fhake againft the
reed ; and the longer that part of the ,
' tongue
RECREATIONS. 433
tongue I L| which is at liberty^ is madct
the deeper is the found. The mould 1 1,
that ferves to fix the fhallot or recd» the
tongue^ tampien, &cc. ferves alfo to fto'p
the foot of the pipe, and make the wind
go out wholly a;t the reed* Laftly, in the
mould is foldered the tube H H, whofe
inward -opening is a continuation of that
of the reed : the form of this tube is dif-
ferent in different ranks of pipes^ The
degree of acutenefs or gravity in the found
of a reed pipe, depends On the length of
the tongue, arid that of the pipe CK, taken
from the extremity of the fhallot, to the
extremity of the tybe^ The quintity or
intenfion of the found depends on the width
of the reed, the tongue, and the tube; as
alfo on the thicknefs of the tongue, the fi-
gure of the tube, and the quantity of wind.
To diverlify the founds of the pipes, a
valve is added to the port-vent, which
makes the wind go out in fits or fhakes.
In Fig, I . X reprefents a flute-pipe of
wood, Z a flute-pipe of metal, Y a trum-
pet-
234 R A T I aN A L
pet-pipe of metal. ThQ pjpes, to pre*
Tent them from falling, pafe tbio' hples
made iu ho»rd$i placed vpon the upper
boards
The pipe* are made to communicate
widi the wind-chcft in the following man-
ner. There are holes hored that go thro*
the upper and lower boards, and through
iht Aider, (when it is drawn out) into
•ihe partition below j fo that any pipes
placed Hpofl thofe holes will then com-
municfljbe with the partition, which, hy its
valve, communicates with the wind-cheft.
But when the Aider is thruft in> its holes
da not anfwer to thofe in the upper
and lower boards, therefore the commu-
nication is flopped, fo that no wind can^et
to th^pipe.
To every large or^an there muft be at lead
two ,pair of bellows, which are marked in
Fig. I . by 9 T, 9 T, O, O, are the handles,
moving upon the axes n niinn. Each of
thefe
RECREATIONS. t^g
fjbcfb bibtiofws <:<^rifts of two bdards, thtf
)bw6ft of which is immoveable ; and in
th&s there ii a valve r, openiilg inwards^
finda &be leadirlgto it> cSilled the convey-
ing tube. There is alfo a hole in this un^
(3er boards from which a tube leads to the
port-vtnt^ which is a fquare tube marked
4, rifing upward, and infer ted into the
linder fide of tht wind*dicft at 2, In Ac
tube leading to the portvent there is A
valve' that opens toward the port-vent^
imd fuflfers the air to go up the port-vent^
imt not to return* Now the handle O bie-
$ng put ^ownji raifes the upper board T,
Itnd the air enters i&rough the valve r, and
^ben the handle is let go, the weight of
the upper board, which carries three or
four poupd to dvery fquare foot, continu-
•idly ^efcending, drives the air through the
j)ort«vent to the found-board ; and as the
^llowB work alternately, one pair is con-
^faintly defcending, which occafions^a con-
^iftual blaft through the port-^ent. In
*|fh|^mber-opgans tliere i$ but one pair of
bellows,
236 RATIONAL
bellows, but they are formed of three
boards, in the manner of a fmith's bel«
' lows, and fo have a continual blaft. All
the internal ftrudure of the organ is con<^
cealed from the fight by the front of the
inftrument, which Hands upon the part be-
tween the numbers 3 and 6 (Fig. i.)
In every organ the number of partitions
L Lt MM, &c« there are in the founds,
board (Fig. i.) that of the valvea V, V j
that of the rollers s, s; or of the levers x,
y» or 8, 9, and their wires : and that of the
keys ABC, &c muft be always eq^aL
Large organs have commonly four or five
fets of keys, befide thofe that belong to
the pedals or large pipes, the Hops to which
are played by the feet. The keys of aa
organ are ufually divided into four 00-
* taves, which are, the fecond fub-odave,
firft fub-oftave, middle oftave, and fixft
oflave. Each oflave is divided into twelve
flops or frets, of which feven are black
and five white j the former mark the na^.
tural
RECREATIONS. 237
tural notes, and the latter the artificial
notes, that is, flats and fharps. The num-
ber of keys, therefore, when there are
four odtaves, mull be 48. Some organifts
add one or more flops to the firft and fe-
cond fub-odaves* The pedals have two
or three oftaves, at (the option of the or-
ganift; fo that the number of flops is in-
determinate. The keys are placed be-
tween G G, (Fig. I.) but the fcheme could
not contain them all. There are alfo as
many handles /, /, &c. rollers R, R, &c.
flidersyjyj &c. as there are flops upon
the organ ; and it muft be obferved, that
between the Aiders f^f^ &c. there are as
many Aiders on the right hand, and the
fame number of handles and rollers, and
other rows of pipes placed between L N,
P Q^ &c. which could not be exprefled in
the figure.
The leaft pipes and partitions are plated
toward the middle of the organ, and
the greateft on the outfidc. The llops
of
43^ ti A t f 5 ]W A t
of an organ have Various denominatiofili
according to the founds they are to pro^
ducej fome of which are diapafon, princi-*
pal, fifteenth, tfwelfth, tearce, corneti
trumpet, French horn, vox humana, flute^
baffoon, cremona, &c. There is likewift
a contrivance to fwell the notes of fome of
the ftops.
When this magnificent inftfument ii
played) the handle O of the bellows is firft
put dpwn^ which raifes the upper board
T, and gives room for the air to enter hf
the valve n Then the other handle O i§
put down } in the ^nean time the board T^
belonging to the firft handle, defcending^
and {hutting the Valve r^ drives the aif^
through theothet valve, up the port^vnet^
and into the wind-cheft. Then drawing
cut any handle, as that of the flute-ftop
p /, which draws out the Aider jT^, all ttef
pipes in the fet L.N are ready to play^ a^i
foon as the keys C, D, E, &c. are put down i
therefore^ if the key D be put down, it
opent
RECREATIONS. 239
opens the correfponding valve m V, thro'
which the air enters into the pipe X, and
makes it found. In the fame manner any
other pipe, in the fet LN, will found when
its key is put down j but no pipe, in any
other fet, will found, till the Aider be drawn
out by its correfponding handle*
The organ is not only the moft grand,
but the moft ancient of all compound mu-.
fical machines. Vitruvius defcribes an hy-
draulic organ in the tenth book of his ar-
chitedurei which was celebrated by the
Emperor Julian, in an epigram. St. Je-
rome mentions an organ that had twelve
pair of bellows, and whofe found might be
heard at the diftance of a mile.
THE
Platk xrx.
T^-^T^
\ z
m
\ Q
• \^ • \ • \ • \
^^. 2
/t^^ff.
^.3
,^23a.
T Hfi
C 5 N f £ N T i
OPTICS.
y^I^NERAL liEFINlTIONS - #*ge t
GENERAL APHORISMS g
P I O P T RI c s;
DEFINITIONS ^
APHOJIISMS 7
Pr'6perti(& of refraSted ligM, apt: i td 3;
•^ftopcrties of lehfes; aph. 4 td 6:
Th^brjr of refraaing tdefcopei ^
X— diir of refleaing telefcqpe^ it
■ ■ ■ .1 of microfcope* 12
Yot„ijL R RE-
Z42 C N T E N T S:
RECREATION I. p.143-
Threcpieccf of flSLoney being placed in a^
veflfel (PL III. Fig*. I.) oat of thcTiewof
a fpcdtator, and water being poured in-^
to the veflel aJl thofe pieces become vi^
fible— by therefra^on-of the light thro?^
the water. ... ,
IL E C R E A Tf 01* IE p.. 15,
optical augmentation.
A fhilling being put \ii a gla& of watepi
^ and a plate placed upon it^the glaft i^*
* turned ovgr with the plate, and tfaerc"^
^ppeaps a ^l^^^mwa pn tij? jpjatf anifc
af^iUmgover it^^l^ theieeing^^^
ling through the top and the fid^ of the
. water at thd fame time^and-tbe different
refradion of the light
t 0'l4 f ENT«. «43
Recreation in, 11.17
optical JuhtraSlhn^
itltree ^mail pieces <£ paptt bftiiig; placed
agamft a wall, (Plate III. Fig. au) a
petfon by fliutting one of his* eyes ^can
fee only two <if them — tfie rays that
comfe from one of the pieecs faUing
always oil the optic nerve, and not oa
the retina. •
REpREATION IV. p. rt
Alternate ittufion,
Afilveir.ieal, yAuesi vit!n^^9»^iMoii-
vex leas, appears {iU^foatelj ongmved
«hd lii dreIiefi-->conQe^re ofk^QcagSb of
tUis remar^l^;pI]|:9oaieay9»:||4$[ft^te)
RECREATION V. p.ao
«
The camera obfcura,
JS. (0nvex lens is placed in the tnndow*
ihutter of a dark room, and a concave
R 2 pafte-
244 CO N T E NTS.
pafteboardt lined with white paper, is^
placed in the, focus of the lens, where-
by the objefts without the room are
painted on the paper, but inverted-
method of making them appear, ered,
page 22 (note) — ^this apparatus im-
proved by a mirror placed in different
pofitions> p. 22 — prefents the moft
pleaiing and natural of all pi^lures 25
RECREATON VI. p. 25
Tojhow the fp^U in thefniis difik^^ by its
image in the camera obfcura.
By placing a fcioptric ball, that is, a ball of
wood in which a lens is fiked, oppofite
the fttni which will throw its image on
the papet'^-^this image to be viewed
through another lens, p. 26
.^/
' . ) '. : ,:
'\
' r
■ I
•
iiVrr 0:1 J
■ J • .
r • ^
■%
t'^3 i: ir
_.- ,.^' .;, .J
*.
■ ": . *J
y
r
fV
RE.
CONTENTS. 245
RECREATION VII. p. 27
7o tnagnify fmall objeSis by means of the
funs rays let into fl dark chamber.
By throwing the rays on a concave mirror,
and holding the fmall objects, iluck on
flips of glafs, near the focus of the mir-
ror, by which mean their images are
refleded on the walL
RECREATION VIIL p. 28
Th( portable camera obfcura.
A plate of gls^fs is placed in a horizontal
frame of wood that is fupported by
four legs, which fold up (Plate HI.
^^S- 3-) Under the frame is a Box,
that likewife folds up, 2^nd at the bot-
tom of it are a tube and a mirror, by
which the objeds are refledied to the
glafs — advantage of this camera over
others, p. 30 — manner of drawing ob-
je^ by this machine P* 3 ^
R3 RE.
^4* C ONTKN^^S. '
RECREATiaN: IX. p. 3a
7h^ magic luntern.
The prigin of this piachine — k 'coiifift^
of a tia box,, at one end of which is a.
concave UHrror ; in the other ead i^
fixed a Jens, and between them is placed
^ lamp : before the lens is fixed a fquare
tin tube in which * there is a groove,
^nd through this groove the glafle^
that contain the obj$(^ are pafled ; iv\
this tube is placed another, that is move-
able, aftd contains t\^ lenfes^ which
throw the objed^ on a cloth — method
of painting the glafles^ p. yj — prppofal
of improving this machine by wfing
moveable objedis ' P* 39
RfiCREATIdlsr X. p.49
Ta reprefent a tempeji by the magic lantern.
By pafling two glafles, on one of which is
paiatcd the . fe^ and Iky, and on th^
othei
t3 O n TENTS. »47
K)ther fhips, (Plate iV. Fig. i and 2.)
through the groove at the fame time,
.»and giving them a proper motion — by
the fame method a battk, and many-
other fubjeds may be exhibited p. 42
R£ CREATION XI- p.4i
The ntbuJous magic lantern.
.At th^ fepttom of a .fqjLiare boK^ whofc
height. is equal to fix times its width,
(Plate IV. J?ig. 34 is placed a chafii^g-
difh c^ hqtxoals, on vrhich iQcepfe is
burnt, and on th^ imoke that comes
vOut of the top of the box is thrpwathe
figures of the magic ^lantern.
RECRJEATIQN ZIL; p. 44
To produce the appearance of a phantom^ on
a box vr pedejial placed on a tabk^
.A common magic lantern, is placed in a
box, (PlatelV. Fig. 4t) in whifeh there
Is an inclined mirrar, that refie^ lihe
R.4 Hglrt
f 4« CONTENTS.
light .of the lantern on the thick fmokfr
of a chafingdifh of coals placed on the
box, and fhows the image refleded by
the gfafs — this Recreation muft be per-
formed in a dark room p' 47
RECREATION XIIL p. 48
STA^ magical theatre.
A magic lantern muft be provided that has
a tube in two of its oppbfite fides, (PL IV.
Jpig; 5.) in one of which tubes there
* miift be feveral grooves, by which the
fubjefts to be reprefeated may be paffed
erther horizontally, afcending, or de-
fcendingi and twaor more of them at
the fame time. In the partition between
the room where t]he lantern is, and that
Virhcre the exhibition is to be feen, there,
muft be placed a glafs, covered with
thin paper^ on which the objedls are to
be thrown — example of a reprefentation
of the fiege of Troy, in five afts,
r* S^-^it is quite ncceflary that the
glaffes
p O N T E^N;T 8. 249
l^lafTes for thefe !exbibi$ions be accurate*
\j painted, p. 6a -
CATOPTRICS-
DEFINITIONS 6%
APHORISMS 63
Properties of plain mirrors, p, 63— of
fpherical convex mirrors, p, 64— of
fpherical concave mirrors, p, 65.
RECREATION XIV. p/67
The boundlefs g'aUery.
Againft each of the twafmalleft eiidaof
an oblqng box (Plate VI. Eig. i.) is
placed a plain mirror, and from oni& of
them the quickfilver 4« taken off for the
fpace of an inch and a half, oppofite
which a hole is made in- the box:, the
top of the box is covered- with glafs,
and between the mirrors are. placed
fcenes properly paintqd,,. which- when
viewed from the hole at the erifl of the
6 box,
252 C (D N T R>4 T«.-
of a ^tal cafe^ and toward the top -of
the cafe is fixed a mirror, by which
the figures of the hours are reflefted to
the part where the dial is commonly
feen. Another dial plate» at the back of
which is concealed an artificial mag-*
net, that is moved by the hand of that
dial> is given to a perfon, who fetting
the hand privately to any houf, puts it
in a drawer at the bottom of the di^I-
cafe, under the firil mentioned dial, and
' looking in at top he fees the reifleGion'
of the dial there, anfwer to the hour at
which he fet the other dial ; the'han^
of the firft being moved, by the attrac-
tion of the magnet in the other, to the
fame hour.
RECREATION XIX. p.8i
J^he box of divination.
A box that contains four cafes, on each of
which a number is wrote, and at the
' bottom of which a magnet is concealed,
' Plate
(f late Vill. Fig, i.) is placed on. a ta-
bie : under that part of the table ar^
placed four:inoveabtexirclۤ5 that Have
each a needier and under them is a
drawer, that (contains a mirror, fo that
by looking into the draper you fee^ by
that mirror, in what order are placed the
boxes that have the numbers^
RECREATION XX. p.84
TAe magical perfpeSiive.
A fmali common perfpedive (Plate VlIL
Fig* 6.) is fixed on a hollow ftand of
wood J in this perfpecJtive is placed a
mirror, which is moved by the inner
. tube> fo a^ to mow any objedl under the
hollow ftand. Three of thefe perfpec-
tives .are fet over three holes in the
top of a box, (fig* 5.) at the bottom of
which is placed a moveable circle, that
is divided into twenty-one equal parts,
and contains a magnetic needle : ' this
box is fet on a table, under which
•'• ■-'^' ^^ ' is
154 C f* t fe f^ t i.
18 concealed a magnetic bar, thalfefeirig
privaiel]^ placed in any poGtioni deters
mines tliiat of the circle In the box,
and confequently brings any of the ob-*
jeds painted on it under the fevieral
perfpCiSHves.
RECREATION XXL p! 93
TAe fenetrathe ferjfedlw^t ^
In a box or cafe that has two prominent
parts or arms, (Plate X. Fig. i.) arc
placed fottr mirrors, and in each bf the
arms is fixed the tube of a perfpcSive
glafs, fo that the objed ijext th? epd of
one perfpeftive, being refleQed by the
four mirrors, is feen at the en4p£^thc
other, and appears as if viewed through
the tNVO perfpedivcs, and ^nfequently
" is perfedly vifibk whea an opaque
body is placed between thofe two per-
fpedives.
kEeRE-
CONTENT!;. 255
RECREATION XXII. p,^^
*Xhe magicmii s mirrors.
Two glafles are fixed in the partition of
a room, at about a foot diftant from
each other: (Plate X. Fig. 2.) behind
thefe giaffes are pl^ed two mirix>irl5, in-
clined in a proper angle, fothat a perfoa
looking into one of them, inftead of fee-
ing his own face, fees that of another per-
ion wbo at the ikme time loc^Suinto the
other glafs. Method xrf" improving this-
Recreatioii, by putting the two glides
»i adjoining rooms, p. 97-— properties^
cf plam Wrrora when placed in dif-
ferent-pt)litions p. pft
R E C R E AT 1 N XXffl. f^ 100
J^olimofio^*
Thefe Ihftrumcnts confift of a tube that
- contains ao inclined mirror, and has an
. , .T ' . «ye-
256 C ON TENTS.
cye-glafs of a proper focus, fo that
while the tube is pointed at one objedt
fon fee anothfet. * By placing an inftru-
ment of this fort at the top of a wall,
while you fland at the bottom, yoii
fee x/^hzt pafTes on the other fide, p. 16I
RECREATION XXlV; ioi
^he enchanted fnirtors:
In four parallel fides of a cubical box are
fixed four glaffes, reprefenting mirrors^
aiid within the box are placed two mir-
rots, that crofs it diagonally. When
four perfons look into the glaffes, each
of them fees, inflead of his own face,
that of the perfon next him, arid ^ho'
appears at the fame time to be placedF
dlrcflly oppofite to him.
RE-
CONTENTS. 257
RECREATION XXV. p. 103
T!he animated optic balls.
This pleaCng piece of optics confifts of
an oblong box, (PI. IX. Fig, 2.) three
fourths of the upper part of which is
divided from the lower by a horizontal
partition, and is decorated with paint-
ings. In the lower part of the remain-
ing fourth is placed an inclined plane,
in the middle of which is a ferpentine
groove, and in the other parts are paint-
ings, or objedis in relief: in the upper
part of this fpace is a mirror, placed in
in a proper angle to refled the objcds
on the plane. At the end of tlie box
is a fmall opening, by which ivory balls,
that may be painted with different
colours, are put in, and running down
the groove in the inclined plane, pafs
out at the bottom, and are raifed to the
fame opening again by a machine placed
Vol, IL S there
26o CONTENTSv
RECREATION XXVIIL p.12^
To defcribe^ on a plam furface^ a deformed
figure^ which Jhall appear regular when
viewed by reJIeSiion in a cylindrical
mirror.
Part of the furface of the cylinder (PI. Xf.
Fig. I.) is to be diyided by lines, inta
twelve parts, in proportion to thofe of
the diameter of the circle CD, Fig. 2.
*Fhe parallelogram, Fig. 3* is likewife
to be divided into twelve equal parts,
and on them a regular figure is to be
drawn, and then transferred to the fame
number of parts, wrhich will be reflect-
ed on the plane DG, by the lines on
the cylinder, and the figure will then
appear deformed, but being feen from
the point of view E, will be quite re-
gular. A fimilar experiment may be
made with prifmatic and other mir-
rors p. 124.
RECRE-
CONTENTS- 261
RECREATION XXIX. p, 123
Optical appearances^
A botde half full of water being placed
near the focus of a concave mirror, ap-
pears not only inverted, but the water
at the top of the bottle and the bottom
of the bottle empty. If the bottle be
inverted and placed before the mirror,
its image will appear: ered, and the wa-
ter at the bottom of the bottle. If while
the bottle is inverted it bp uncorked,' it
will appear^ that whije the upper part
is emptying the bottom part is filjine;.
RECREATION XXX. p, 128
7 he perfpeSlive mirror.
At one end of an oblong box (Plate XII.
Fig. I .) is placed a concave mirror ; near
the upper part of the oppofite end a
hole is made, and about the middle 6f
the box is placed a hollow frame of
S 3 pafte-
262 CONTENTS.
pafteboard, that confines the view of the
mirror. The top of the box next that
end in which the hole is made is co-
vered with a glafs ; and under the hole
are placed, in fucceffion, diflFercnt pic-
tures, properly painted* which are
thrown into perfpedive by the mirror,
and produce an appearance that is highly
'pleafing,
RECREATION XXXI. p. 130
To fet fire to a combufiible body by the re^
fieSlion of two concave mirrdrs.
Thefe two mirrors (Plate XIL Fig. 2.) are
placed at a confiderable diftance, and in
the focus of one of them is put a live
coal, in that of the other fome 'gun-
powder, and by the blowing on the
coal, the gunpowder will take fire,
thoughthe diftance between the mirrors
be feveral feet.
RE-
CONTENTS. 263
RECREATION XXXII. p. 132
The real apparition.
A hole is made in a partition, (Piate XF.
Fig. 3.) and behind it is placed a large
concave mirror, and a llrong light, that
muft not be vifible at the hole. On the
fame fide of the partition, and dire£tly
under jhe hole, is fixed, in an inverted
pofition, the objeft that is to appear
without the partition. Aperfonbeing
placed in a proper point of view will fee
the objecft on the outfide, and in an
ere£t pofition — The figure of an abfefit
or deceafed friend may be made to ap-
pear by this method, p. 1 34— The ima-
ginary coinbat by a concave piirror,
G H R O M A T I G jB,
DEFINITIONS p. 137
APHORISMS 138
*S 4. RE-
264 CONTENTS,
RECREATION XXXIII. p. 140
Out of a fingle colour lefs ray of light to pro^
ducefeven other rays^ which Jhall painty
on a white body^ the feven primary colours
of nature.
-A round hole is made in the window-fhut-
ter of a dark room, and the ray of light
that enters at the hole, falling on a
prifm, is refradled, and being thrown on
a paper placed at a proper diftance,
forms an oblong fpedrum that exhibits
all the primary colours of nature.
RECREATION XXXIV. p.i4a
From two or more of the primary colours to
compofe others^ that Jhall^ in appearance ^
refemble thofe of the prifm.
By mixing any two of the primary co-
lours, as yellow and blue, the interme-
diate colour, green, will be formed ; but
thefe mixed colours, though fimilar in
appearance to the primary, yet when
viewed
C ON TENTS. 265
viewed through a prifm, are refolved
into the colours of which they are com-
pofed.
RECREATION XXXV. p, 144
Out of the three prirfiary colours ^redy yellow^
and blue J to produce all the other prifmatic
colour Sy and all that are intermediate to
them.
Three panes ofglafs are divided, each of
them into five equal parts, and over
thofe parts are pafted a different num-
ber of papers, painted either red, yellow,
or blue (PI. XIII. Fig. 2.) When one
of thefe glafTes is put in a box, open at
two oppofite ends, all the gradations
of the colour it contains are vifible ;
and when two of them are placed toge-
ther. Fig. 3, the intermediate colour ap- ,
pears, with its feveral degrees.
RECREATION XXXVI. p. 147
By means of the three primary colour Sy, red,
yelloWy and hlue^ together with light and
7 Jbade,
266 CONTENTS.
Jhade^ to prvduce all the gradations i>ftlie
prifmatic colours.
On feven fquare panes of glafs papers ar?
palled that contain all the prifmatic co-
lours, and over them are put a diflferent
number of pieces, tinged with a deep
ihade^ and they are then placed in a bpx,^
in the fame manner as in the laft Re-
creation. Method of pripting in co-^
lours, p. 148,.
RECREATION XXXVIL p. 150
The magical prifm^
A ray of light that comes through a hole
made in the window-fliutter of a dark
chamber, falling on a glafs prifm, (Plate
XIII. Fig. 4.) is refraded on a hollow
prifm of wood, that revolves on an axis,
and in whofe fides figures are cut. As
this prifm changes its pofition with re-
gard to that of the glafs, the figures
cut out will appear white, yellow and
red, or blue arid violet. *
CONTENTS. 267
RECREATION XXXVIH. p. 152
T^he folar magic lantern.
A fmall box that is ,open at two oppofite
fides, is placed again^ a hole of the
fame fize in the window- Ihutter of a
dark chamber that faces the fun. Thro*
this box are pafled, by a groove, pafte-
board blacked, and through which dif-
ferent figures are cut. Thefe figures,
when viewed through a prifm, appear
to be painted with the moft lively co-
lours in nature. This Recreation may
be diverfified by pafting papers, tinged
with different colours, over the figures
in the pafteboard.
RECREATION XXXIX. p, 154
7/ie artificial rainbow^
Oppofite a window on which the fun
fhines, a glafs globe, filled with water,
is fufpended by a fl:ring that pafles over
a pulley ; and when it is drawn up to a
certain height, which may be found by
trial,
268 CONTENTS.
trial, the colours of the rainbow will ap-
pear in it : w^^en it is drawn up a little
higher the colours difappear, and when
it is drawn up ftill higher they appear
again, and at laft totally difappear. The
phenomena of the natural rainbow ex»
plained by this ejcperiment, p. 155,
RECREATION ja. p. 158
^he prifmatic camera obfcura^
Two holes are made in the Ihutter of z,
dark chamber, (PlateJilll.Fig. 5.) and
againft each of them a prifm is placed,
in fuch manner that both their fpec^
trums arc caft upon the fame fpot. Se-
veral papers, of the fame dimenfion
with the fpedtrums, have lines drawn on
them, parallel to the divisions of the
colours, and between thofe divifions fi-
gures are cut out, which then appear to
be painted with all the primary colours.
This Recreation may be diverfified by
turning one of the prifms round; and
by looking at the fpedrums through an-
other prifm, p. 159.
RE^
CONTENTa 269
RECREATION XLI. p. 160
T^he diatonic Jc ale of colours.
The fun's fpedrum is to be largely re-
fraded on a paper', and the divifions of
the feveral colours fet ofF, when they
will be found to correfpond to the di-
vifions of a mufical chord for the notes
of an o^vc,
RECREATION XLIL p. 162
Colorijic mufic.
The furface of a hollow cylinder (Plate
■ XIV. Fig. 2.) is divided vertically into
fix equal parts, and horizontally into for-
ty-one parts; in each of the latter parts
fpaces are cut, over which are pafted
papers that are painted with the feven ,
primary colours. At the bottom of
this cylinder is a wheel, an endlefs
fcrew, and a nut ; and when it is placed
.in a cafe, Kg, 3, the endlefs fcrew is ^
turned
270 CONTENTS.
turned by a handle, which turns the
wheel, and raifes the cylinder by means
of the nut at bottom, the height of five
of its horizontal divifions, and confe-
quently fhows the feveral colours it con-
tains at the eight apertures made in
the front of the cafe. A lamp ie fuf-
pended from the top of the cafe, which,
hanging within the cylinder, ihows the
colours that anfwer to the notes of mu-
fic, and the length of thofe colours cor-
refponds to the duration of the notes.
PERSPECTIVE RECREATIONS- J
RECREATION XLIIL p. 168
To draw on a plain furf ace an irregular fi-^
guriy whicby when Jeen from a proper
point of view, will appear Jimilar to a
given figure.
A parallelogram is divided into forty-eight
equal parts, (Plate XV. Fig. i.) on
which the regular figure is drawn, and
its
CONTENTS. iji
its feveral parts tranfpofed, to art ecjtial
number of divifions in a trapezium,
where the figure will appear deformed,
but when feen from a proper point of
view, quite regular. The correfpoAd-
ing parts in the parallelogram and tra-
pezium are to be numbered, p. J72 —
Thefe figures appear to great advan-
tage when painted on the fide of a gal-
lery, p. j 74.
RECREATION XLIV. p; 175
T^o draw an irregular figure on a plane ^
which being feen from two oppofite points
of view, Jhall reprefent two different re^
gular objeSls.
The two regular figures are to be firft
drawn on the two parallelograms, (PI.
XVT. Fig. 3.) and then transferred to
the divifions of the parallelogram. Fig. 2.
On a board, Fig. 4, of the fame fize
with the laft figure, lines are cat, in,
which
2^^ CONTENTS.
which a paper, Fig. 5, is pa^ed, and the
diftorted figure on it; which wlwnfeen
from two proper points of view, will
prefent two regular figures.
RECREATION XLV. p. 181
T!o draw on the bafe of a cone an irregular
Jigure^ which Jhall appear y when Jeen from
a proper point of view ^ not only regular^
but elevated above the furface of the
cone.
The cone is placed in a board, (PI. XVIL. ^
Fig. I.) with its bafe upward, and at
one end of it is fixed a perpendicular
plate of glafs, on which the regular fi-
gure is drawn. At the point of view
a lamp is placed, by which the figure
on the glafs is thrown on the bafe of the
cone, and there traced. The lamp and'
glafs are then taken away, and the diC»
torted figure, when feen from the point
of view appears not only regular, but
ereft^
d 6 N t E N t §. 27J
fereft, and in the fame fituation it was
bn the glafsi
RECREATION XLVI. p. 186
To draw 9 eafily andcorreBfyy aland/cape^ or
any other obje^^ without being obliged to
obferve the rUles ofperfpedHveyandwith-^
out the aid of the camera obfcura.
in the largeft end of a box (Plate XVI L
Fig, 3.) there is a frame, divided into a
number of eqiial divilions, and in the
bppoiite etid is a tube. This box is
fupported on a ftand. You are provided
with a paper that has the fame num-
ber of divifions as the frame in the box,
and looking through the tube you tranf-
fer the feveral objects feen through the
divifions of the frame to thofe on the
paper.
kECREATION XLVIF. p. 189*
Illuminated profpedfs.
The top of a printj properly painted, is cut
off, and put. in a frame, and the lower
part in another frame. Thefe two frames
VoL^lI. T are
274 C O.NTJE ;N.T^^;
are placed in a box, (PI. XVII. Fig. 5.]^
at different diftances, an4 bfhipd ijiqjx^
lights are fet, and when they are viewed
from the front of the box, and there is-
no other light in the room,^ they afford^
a very pleafmg appearance*,
RECREATION XLVIIL p. 191
T^ranfparent illuminations.
* ' .1
Thofe parts of a print where the light is ta
appear are cut through with a fine tqoL
The print is then put in a frame and
placed in the box defcribed in thelaft
recreation : behind it is a yellow tranfpa-
rent paper, and behind that are lights.^
Thefe fcenes are to be moveable, fo as to
' repirefent a fucceflion of objeds dif-
ferently illuminated.
. A C Q U S T I G S.
DJEF IN IT ION S p. 195.
A P H O R I S M S 196
Nature of fonorous bodies, aph. i to 5.— •
Vibrations of chords, aph. 6 to 9.^ — Pro-
pagation of found, aph. 10 to 14. —
Strength and refleiSioa of found, aph..
I5,ftnd 16. R E-^
-5
CO N T E NTS. 2fs
RECREATION XLIX. p-2oi
TAe eoHpiles^
A iii»ll,»eta5 globe, with a flendcr heck,
h thrown, when hot, into a veffel of
water, ju^dwhen it is put on.a.^re the
' water rufhes put with a great nqife — thia^
phenomenon improved by fixing the
calls ufed by fowlers to the necks of
thel^ eolipiles.
RECREATION L. p. 202
The communicative bujis.
Two tufts are placed on pedeftals on the
oppofite fides of a "room, and from the
mouth of the one there goes a tube un-
der the floor, to the ear of the other.
Therefore, if a perfon fpeak into the ear
of one buft, another perfon, who ap{)lies
bis ear to the mouth of the other buft,
will hear diftindly all the firft utters ;
and at' the fame time other people, in the .
middle of the room, will hear nothing
of whatpafles.
T 2 RE-
2y6 C^OhiTE N f 'Sv
RECREATION LI. p. 203
. . T/ie oracular head*
This recreation is performed by a fingle
head, and tubes, that go from the ear
and mouth of it, to a room underneath,
where a confederate hears what is faid,
and returns an anfwer; and there are
♦ wires by which the eyes and lips of the
buft are moved at the fame time.
RECREATION LIL p.a64
T^he folar fonata.
A barrel organ is placed in a cafe, that has
a glafs front, behind which is a tube with
. fpirits, and on that a cork floats, whicjb,
. .wl)€ai it rifes.to a certain point, by the
:\^x. of the fun, lifts up acatch, andfets
th?. organ in play; but when the ma-
• chine, is carried into the cold the fpirits
fmk, and the.catch again flops the organ.
RECREATION LIII. p. 207
An automatons liarfjichord.
Tliire ;4re wires that go from the un^er
part of the keys of a harpfichord, and a
barrel
qO H-TEN T8. 277
f^arrel with pins, that take the ends of
thofe wires. Round the axis of the bar-
rel goes a firing, that paffes under the
floor, and communicates with a fmoke-
jack, by which the harpfichord is playe4
inceflantly.
RECREATION LIV. p. 209
A vmtofc^l fymphony.
Oji the top of a.houfe there is a vane, (PL
XVIII. Fig, 3.) at the bottom of which,
and within the roof of the houfe, is a
wheel, that communicates, by other fmall
wheels and pinions, with a large barrel
in the room underneath : to this barrel
a number of flops are fixed, and clofe
to it are hung twelve bells j therefore,
as the vane is turned by the wind, the
feveral fmall wheels being put in mo-
tion, turn the barrel, and by making it
ftrike the bells, according to the pofition
©f the flops, play the fymphony.
IIEGRE^
«7? COjN T E-MTS.
RECREATION l^V, p-ati
T'A^ noSiurnal reveiilem.
Op the circumference of a wheel areplaccfl^
a numBer of tells, and round its axis
is wbund a rojpe, at the end of wfiich
18 faftened a weight, that refts upon one
end of a moveable lever, and is ba-^
lanced bya hollow cone filled with fand|
hung to thc'other end of the lever, hut '
as the fand runs out the weight defcends,
and by turning the wheel rings the oeils,
RECREATION LVI. p. 8^4
A mttfical cafcade.
A l^fgc wheel is placed under a cafcade,
the water of which is confined to. the
ends of the wheel ; the middle of this
wteel confifts of barsf in which flops
are placed, that* by ftriking a certain
number of bells play one or more titties,
at pleafure.
. RECREATION LVill p. 616
Reverbetated founds. -
Canftrudlion of a whifpering gallery — the
nature of echoes, p. 2 1 7— of reverberated
echoes, p. 219/
CO N TE I^T ST^ 279
RECREATION ' LVin^ p 220
7%^ converjivejiatue.
There are two large concave mirrors, and in:
the focus pf one of them is placed the fi-
gure of a man (PL XVIII. Fig. 5.) The
other mirror is placed behind a partition^
in which is an opening, concealed by a
^au!ze, Wl^en a perfon ,fpeaks ipftly in
the ear of the ftatue, which is e?(a<3Jy
in the focus of one pf the piirror^j an-
other perfon placing his ear in the fo-
eus of the other mirror will hear dif-
tindly what is faid, and anfwqring foft-
fy at the fame point will be heard by
the firft perfon.
RECREATION LIX. p;2a3
The great organ.
The body of this noble inftriiment con-
fifts of a wind-cheft, (PI. XIX. Fig. (.)
over which is placed two boards, that
form what is <;alled the found-board.
In the undier .fide of ^hp Ipwer boftgdare
fevered partitions, apd; in iti upper fide
• »• •: ......are
28o CONTENTS.
are cut channels^ in which Aiders str€
placed, in a tranfverfe pofition to thd
partitions. There are holes made thro'
the upper board,fliders, and under board,
into the partitions ; and in the holes of
the upper board the pipes are placed that
produce the founds. There are two pair
of bellows, by which the air is forced
into the cheft. When any one of the
Aiders is drawn out, its holes correfpbnd
with thofe in the upper board and in the
partitions. At the front end of each par-
tition is a valve, under which i$ a hole
into the wind-cheft: thefe valves are
conneSed with the keys of the organ by
wires, fo that when a key is put down
it opens a valve, and the airruflies into
the partition, and the Aider being drawn
out, it pafles through the holes in that
and the upper board into the pipe placed
over it, and makes it found.
THE END OF THE SECOND VOtUME*
Live Music
Archive
Librivox
Free Audio
Metropolitan Museum
Cleveland
Museum of Art
Internet
Arcade
Console Living Room
Open Library
American
Libraries
TV News
Understanding
9/11